107 Comments on Furnace Troubleshooting (the first step)

Charles on Mon, 5th Feb 2007 3:29 am


Was having problem with no air forced coming through ducts
in bedroom. Removed furnace to clean and check for duct blockage.
Found medal tape had fallen off and was restriction flow. Fixed that
problem, cleaned fan and reinstalled furnace. Hooked everything back
up except the thermostat wired. Learned long ago to jump the wires out at
the furnace and check it before closing the compartment. Worked fine. Finished
hooking everything up and closed compartment. Turned on thermostat and NOTHING
worked. No heat, a/c or fan. Pulled the thermostat, took off the furnace
thermostat wired and hooked them together. Furnace worked. Haven’t finished trouble
shootong the thermostat yet. Long process for a solid state thermostat with a/c,
fan and furnace all on one thermostat. Even with furnace wires disconnected,a/c
and fan will not work. Seems 12 vdc comes through furnace. Any sugestions? What
little troubleshooting I have done, nothing makes sense. HELP!!!

[Reply]



Anonymous Reply:
November 15th, 2008 at 8:37 am

CHANGE TSTATE

Chris on Mon, 5th Feb 2007 10:00 am


Hi Charles- the first thing I would look at is which wire hooked to which from the furnace to the thermostat.
One thermostat wire out of the furnace will be “hot” (+12v), and if it is not hooked to the correct thermostat lead, the thermostat will not have 12 volt power to operate.

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Jean on Sat, 24th Mar 2007 10:02 pm


I use a heat pump/propane furnace. In this weather the heat pump always works but when it is colder the propane comes on and a blue light on my colemane revcon thermostat comes on. Lately a red light has been coming on. It says emg above it. It stays on and circulates the air to keep temp stable but is just blowing air. no heat. Any ideas?

[Reply]

Chris on Mon, 9th Apr 2007 3:09 pm


Hi Jean,
I hate to say it, but I am unfamiliar with that type of thermostat in an RV, and cannot find any information about it on the Coleman website (or in my service documents).

– Chris

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BOB on Sun, 9th Sep 2007 7:18 pm


HI CRIS,
I HAVE A Coleman THERMOSTAT WITH A 2 AMP FUSE THAT BLOWS ABOUT IN ABOUT 5TO 10SECONDS AFTER THE FURNACE FAN 12 VOLT MOTOR STARTS.IT IS NOT CONNECTED DIRECTLY TO THE BATTERY. THIS THERMOSTAT ALSO WORKS THE AC WHICH WORKS FINE.ANY IDEAS AS TO WHATS BLOWING THE FUSE?? THIS IN AN RV. THE FURNACE IS A EXCALIBUR 8500
BOB

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bob on Fri, 19th Oct 2007 12:38 pm


My father-in-law has a 37′5th wheel forgot the model? but it has a sububan lp furnace.We had it going and worked well but after we brought it to his lot now the pilot would not stay lit.After some investigating found a bees nest in the exhaust.We pulled it out with a bent clothes hanger then blew it out with air.Now it wont stay lit at all

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J on Sun, 11th Nov 2007 6:34 pm


Hello,
My propane furnace will not keep the pilot light lit after it is finished running. It will make a click sound and the pilot will go out. I just changed the thermocouple two days ago and it did not solve the problem. Any insight will be greatly appreciated. Thanks,
Jeffrey

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Chris on Wed, 14th Nov 2007 5:35 pm


Hi Jeffrey,
A couple of things to check- the pilot assembly may need to be cleaned, and sometimes if the pilot is set too high, it will starve for oxygen just after the burner shuts off, and go out. The flame should *just* envelope the end of the thermocouple.
But.. in some furnaces it is near impossible to actually see the pilot flame.

– Chris

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Joe Pazzelli on Thu, 15th Nov 2007 2:03 pm


I’ve got an old Coleman 4225A furnace in a 1976 Winnie. Was running great until this fall(deer season). It is burning very rich, soot coming out of exhaust and too hot in heat exchanger. Pulled unit to check for any blockage or obstructions. None found. Both fans working well, just replaced the motor two years ago. Can’t adjust for a good blue flame as before. Very tall flame too tall, which starts out blue but too much yellow. Could it be an air leak or has the General Control 4225A809 gas valve gone bad? Gas stove and frig work okay, which I think leaves out main gas regulator.

[Reply]

Chris on Thu, 15th Nov 2007 7:35 pm


Hi Joe,
Generally that is sign of either too much fuel or too little air. Did it run OK after the motor change? If the motor was running backwards, it would still work, but not put enough airflow through. Likewise the combustion blower wheel could be installed wrong.
If I recall correctly, that unit has a cast iron burner- the slots in those burners are very prone to blockage by rust, which blocks the air flow as well.

–Chris

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Joe Pazzelli on Fri, 16th Nov 2007 1:24 pm


Thanks Chris.
The unit ran fine after the motor change out, good clean blue normal size flame on all three burner sections. It does have a cast iron burner. I’ll check for blockage there. The only other thing is can I still get a gas control valve for this unit or will I have to replace the furnace?

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Chris on Sat, 17th Nov 2007 7:41 pm


Hi Joe,
I really don’t think the gas valve is the problem- I would bet on the slots in the burner being plugged up.
It’s been a while since I services one of these, but I *think* that the slots are wide enough that they can be cleaned with a hack saw blade- you don’t want to make the larger, just clean them out.

– Chris

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Joe Pazzelli on Mon, 19th Nov 2007 7:33 am


Thanks Chris,
You were right on the slots being clogged. I remember cleaning them out when I replaced the motor. Unfortunately when I put the unit back together, the pilot won’t stay lit so I’m getting a new thermocouple today; hoping to fix all my problems. As for the valve, I was told that they are no longer available. I just wanted to know if I could still get one.

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margaret on Thu, 29th Nov 2007 9:31 am


I HAVE A WALL FURNACE AND A MECHANICAL THEMOSTAT. I CAN’T GET MY THEMOSTAT
TO COME ON. I CAN GET THE WALL FURNACE ON BY JUMPING IT. I CONNECTED A HOT
WIRE TO ONE OF THE PLACES WHERE I JUMP IT AT AND WHEN I DO THIS THE THEMOSTAT
WON’T TURN OFF. I HAVE TO GO BACK TO MY WALL FURNACE AND DISCONNECT THE
HOT WIRE FROM WHERE I JUMP IT AT TO TURN IT ON. MY THEMOSTAT IS A MECHANICAL
ONE WITH MERCURY. CAN YOU HELP ME OUT WITH THIS PROBLEM. I NEED TO BE ABLE
TO TURN MY THEMOSTAT OFF AND ON WHEN I WANT TO AND IF WANTED TO LEAVE IT
ON THEN I COULD ALSO AND NOT WORRY ABOUT IT. I JUST WANT IT TO WORK RIGHT.
ANY SUGGESTIONS WOULD BE GREATLY APPRECIATED VERY MUCH.

THANK YOU VERY MUCH. I WAIT TO HEAR FROM YOU.

SINCERELY,

MARGARET,
mchwalowski@yahoo.com

[Reply]

Chris on Fri, 30th Nov 2007 8:01 pm


Hi Margaret,
I guess the easiest thing would be to replace the thermostat, but you might take the cover off and look for a small adjustment called an anticipator- which will be a wire with a slide connector on it. Sometimes they are a round assembly, sometimes they are straight. If you move the slider down to zero, often that will “fix” a problem like that (the wire sometimes gets corroded, and moving the adjustment can help.
To replace it, a popular replacement is the Hunter model 42995, which is available at WalMart for about $20. It is an electronic model, but will work fine for furnace only- just hook the 2 wires to the RH and W terminals.

–Chris

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Sherii on Mon, 3rd Dec 2007 8:38 pm


Hello, I have an Excalibur Hydroflame 8500 IV which seems to have lost it’s muscle. Everything works fine as it always has - with the exception that it doesn’t seem to heat my bus up like it used to without consuming excessive amounts of propane. I think that the flame must not be hot enough anymore but I can’t see it from any angle inside or out, I can however hear the difference if that makes sense? Every winter (this is the 5th) I acclimate to the familiar “tiger torch roar” but it is a sub-sound under the blower motor this year. Plus the air just doesn’t feel as hot as it used to coming out. From my RV repair books I think the burner/flame has issues but they don’t show how to get at the burner of this model, nor does the 3 page Atwood installation manual. Is there an easy way to determine if this is the problem? I live in the bus so leaving it at a shop is out of the question - and pulling the furnace out would have to happen while it’s snowing because it won’t be warming up here again until May… Thank you for any suggestions or directions on how to see or clean or adjust my Hydroflames Flames!

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James on Thu, 6th Dec 2007 1:12 pm


Hi, I have a Coleman [High efficiency gas-fired furnaces tubular heat exchanger series Model: P*UR / G9T-UP/ FG9-up (upflow) 40 - 140 MBH input] and it seems that our furnace turns on, but shuts off after 1 or 2 minutes of heating. it seems to give 6 red flashes when i check the furnace control dignostics, and in the manual it seems that 6 red flashes mean, the pressure switch opened 4 times during the call for heat?? and we have no idea what they mean by delay on or off mode. can you help me with this problem?

Sincerely James

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Michael on Tue, 11th Dec 2007 4:04 pm


I have an older Lennox forced-air furnace with a standing pilot. For days the pilot would randomly go out. I replaced the thermocouple, cleaned the orifice, and ajusted the small hood on the pilot flame opening.
The thermocouple it sitting nicely in a strong blue flame, and once the pilot is lit it will stay lit for five or so minutes and then you can hear the solenoid release the gas valve and it closes. End of pilot.
Any idea what this problem might be? When the furnace runs, it runs well. The gas valve just won’t stay open to keep the pilot going. I hope it’s not the gas valve.

Thanks!

Regards,

Michael

[Reply]

Chris on Tue, 11th Dec 2007 4:17 pm


Hi James,
I’m afraid I don’t have any service information (or, for that matter, any experience ;)) with home type furnaces.

But.. Michael- I would almost be tempted to replace the thermocouple again, as I have seen brand new thermocouples fail. They wrok using two different metals, which generate current when heated, but every now and then the junction between these metals can open up when heated.

– Chris

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Michael on Tue, 11th Dec 2007 4:57 pm


Thanks Chris. I’ll try that. Ggrrr.

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Chris on Tue, 11th Dec 2007 6:15 pm


Hi Michael,
One more thought- the connection of the thermocouple at the valve is actually an electrical connection- if you look at the end, the very tip is insulated from the outside of the tube by a thin insulator.
The thermocouple should be hand tightened firmly, plus a quarter turn- if the pilot doesn’t stay lit, give it another quarter turn. Over tightening can crush the small insulator.

– Chris

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Ron Bennington on Mon, 17th Dec 2007 3:39 pm


Hey Chris,
Just bought a used RV, suburbane furnace. have got it to light off twice in two weeks of trying every day, 6-7 times a day. Removed furnace, removed board took it to RV repair shop, board tested ok. I get fan, I get spark, just not lighting the pilot.

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Kenny on Sun, 30th Dec 2007 5:22 pm


I have a Suburban SF-30 in an Outback 33′ that is 1.5 years old and on it’s second cool season. It always seemed to a little temperamental when igniting but has generally been trouble free. Today, not so. Everything starts and runs but no ignition takes place. Coincidentally, I had a tank switchover take place about the same time it quit. The switchover appeared to be normal as I have gas at the stove, frig, and hot water heater. I broke the line at the heater and have it there as well. Both tanks share a common regulator on the output of the switch. As for correct pressure, I don’t have a manometer but judging from the stove burners, it looks okay. ( Side question, just how much of a pressure drop can a furnace stand before it refuses to work??) Could the switchover have starved the furnace and damaged a gas valve or something? Because of it’s location, it appears that it has to be completely removed to service the components so I don’t want to do that unless absolutely necessary. Any input to a possible solution would be appreciated. Thanks.

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rick on Wed, 2nd Jan 2008 11:59 pm


I have the exact situation as Kenny above blower blows plenty of propane, igniter tries three times but will not fire furnace. Please comment, ASAP I’m getting cold.
thanks,
rick

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john on Thu, 3rd Jan 2008 9:50 pm


Well let’s make that 3 of us, I have 05 TT with a Suburban sf30f, stove work great, blower comes on then 3 or 4 popping sounds then the blower shuts off(this is in about 10 time span)…I going to wally world and buy a radiator heater

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glen on Sun, 6th Jan 2008 10:55 pm


Make that four of us. I have a Suburban furnace that’s be working intermittently. Now it won’t work correctly. The fan comes on, I hear the igniter, smell the propane, but no ignition.

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FurnaceGirl on Mon, 7th Jan 2008 3:23 am


For the guys up above:

Unlikely this could help all of you but may be of help so I offer it up - I had a similar problem with my furnace last year that was due to an overfilled propane tank. Electronic lockout can occur if the gas pressure coming is too high, it’s a built in safety feature. Another similar situation my first year way back was flies and spiders camping on the burner - they clog the combustion process - after I got it lit a dozen times or so (each time it stayed on a few seconds longer) they were burnt off and I had no problems.

Good Luck!

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glen on Mon, 7th Jan 2008 10:24 am


FurnaceGirl,
Thanks, but no bugs in the burner and I’ve tried with two different propane tanks - one about 1/5 full and the other full (well, “OPD” full).

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John on Tue, 8th Jan 2008 6:38 pm


I have a 8500-iv hydro flame seies furnace in my 2003 Toy hauler.I have trouble shot to the best of my knowledge,the blower works,electrode works,but no power from ignition board to valve.also after electrode stops trying, red light on ignition board comes on.Any help would be appreciated.
Thanks,
John

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Roadless Warrior on Wed, 9th Jan 2008 3:05 pm


Sounds like your board may have died - common problem, not too hard to fix. Go here and search your model number for T-shooting and repair help.

Cheers (-:

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benjamin gee on Thu, 17th Jan 2008 1:22 pm


i have a Suburban model NT-34L furnace. initial problem was a popping sound each time the burner lit. As i sleep with my head over the furnace, this got to be old in a hurry. I initially replaced the gasket around the burner access thinking that an air leak might cause the popping. still popped. I pulled the furnace, cleaned the blowers (intake and exhaust), removed the mud dauber nests, removed the burner and cleaned it as it 4 slots blocked with rust. reassembled furnace, reinstalled and guess what- furnace still pops upon ignition. It also will pop intermittantly if i let the furnace run. Gas flame is blue, some orange/yellow above the burner, flame kind of ripples right on the cast iron burner. no separation between flame and burner. Please advise and thank you.

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Rich A on Sat, 16th Feb 2008 2:16 pm


Sounds like we may all have a similar problem. I have a Suburban N-30M furnace with the same problem as mentioned above. Solenoid energizes but propane is not flowing. I replaced the solenoid valve.. still not working. Tested ewverything on the bench and found that the solenoid although clicking when powered, is not allowing flow when energized under pressure. If solenoid is energized and then the propane is thurned on, I get flow. Confused as to why this is happening. I even tried botha 20psi and 10psi propane regulator. Any suggestions would be appreciated.

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Rich A on Sat, 16th Feb 2008 3:54 pm


I found the answer to the post I made previously. The unit had been dropped off at my house by a friend who couldn’t fix it. I replaced the transformer and then ran into this “propane flow problem”. It seams he connected a supply line/regulator he had laying around to test the unit. This regulator was for 20 psi. Some research showed that the solenoid is only rated for 1.5 PSI. The hard piped line in the camper is regulated at this lower pressure and everything now works fine.

[Reply]

Jack on Wed, 27th Feb 2008 4:46 pm


Chris,
My furnace blower fan just stopped working today. I tried/tested the furnace a couple more times with the thermostat igniting the furnacw with natural gas burning fine—just no blower fan. is the problem most likely a fan motor gone out or could it be something else.

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Chris on Wed, 27th Feb 2008 7:54 pm


Jack,
Is this furnace an RV furnace? The only reason I ask is that in new RV furnaces, the burner cannot ignite until the blower is running.
If it’s a house type furnace- I’m not that familiar with them, but usually the blower is controlled by a fan switch, which turns the blower on when the heat chamber reaches a set temperature.
If it’s an RV furnace, I would suspect the fan relay.

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Bobby Simpson on Tue, 4th Mar 2008 11:00 am


I finally got the step working after another cleaning of the
large 4 way plug and the door switch. It seems to stay out now.
Thanks for the input.

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mike on Tue, 4th Mar 2008 10:46 pm


I have a rudd furnece and it will be runing then it seems like a air pocket in the gass line and then theres 3 or 4 sucksons then the furnece shuts off then you here clicks then it starts back up right away and will stay runing and it will do this every now and then can you please help me thanks mike

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Steve Rightnar on Sun, 16th Mar 2008 9:28 pm


Hello:
I have a Suburban SF-20F and nothing happens. No blower no clicking nothing and its just past the warantee. I checked that it is getting power and the power is there. The thermostat is putting out voltage when I switch it to the heat setting. I was going to bypass the control module and put the hot wire right to the blower but I dont want to try things without some advice. Thanks for any help!!!
Steve

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Steve P. on Thu, 3rd Apr 2008 12:14 am


I have a Suburban floor furnace in our 1992 Sandpiper. It has electronic ignition. When I turn the thermostat on the fan comes on and only blows cold air. I have been told this might be the thermostat but I do not know how to test it. Can anyone help. Thanks

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Dale Randall on Thu, 3rd Apr 2008 5:38 pm


I wish that I would have found these posts before I tryed to fix my Suburban SF-30F furnace. The theromstat would start the fan, but there was no burner ignition. I removed the furnace. I took the burner apart and cleaned out the sand. I re-set the ignitor gap to 1/8 inch per the manual. After trying many different things, I jumpered the two blue thermostat wires instead of hooking up the thermostat. Then the furnace would start and light every time! Maybe a bad thermostat? I hooked up the thermostat again and found that the voltage to the limit switch was 7 to 8 VDC even when my converter was putting out 13.6 VDC, which is normal. I found a loose rivet in the Suburban thermostat, which I soldered (this can melt the plastic).
This fixed the problem, but I still couldn’t explain why the thermostat was only getting 11 VDC when the furnace was running (10 VDC at the limit switch. I found a two volt drop on the positive power wire to the furnace, but only 0.25 volt drop on the ground return wire. I replace the power two wires with about 10 feet of # 14 wire so the furnace now runs at full voltage.

[Reply]

FMB on Fri, 4th Apr 2008 11:54 pm


In my ‘04 Arctic Fox 24-5N, there resides a Suburban Furnace. It heats the
5th very well and will be 5 years old in July.

Since this is my first experience out of a tent or house, I thought my
furnace was working properly all along, till late last year. That is when
the steps in the furnace’s processes changed and made me think it may have
been busted from the get-go.

With the thermostat set at a temp higher than the room temp, I switch the
thermostat from ‘off’ to ‘heat’. Here are the steps the furnace took the
first 4 1/2 years;

1. Instantly, the blower motor comes on. You can feel the air blow out the
heater outlets in the floor.
2. It heats the trailer very well and when it reaches the thermostat temp,
the gas turns off and the blower continues to run.
3. The blower runs for about 2 min. (I understand this to be the ‘cooling
down’ time so the furnace doesn’t stop hot) At the end of this 2 min, the
blower power goes off and the blower begins to wind down.
4. Before the blower stops, it kicks back on and runs for another 2 min, at
the end of which, it powers down.
5. Before the blower stops, it kicks back on AGAIN and runs for another 2
min at the end of which, it powers down and stops.
6. The heater is off, waiting for the thermostat to tell it to turn on
again.

What changed to make me think this wasn’t normal?

Sometimes, the heater will skip steps 4 and 5, or will repeat step 4 several
times. The heater will cycle at least once, mostly 3 times, but up to 7
times (that I know of). The air is blowing room temperature after the 1st or
2nd cycle.

Relay???

[Reply]

Chris on Sat, 5th Apr 2008 8:08 am


Hi FMB-
I would guess that the furnace has been cycling on the limit switch- the thermostat is still calling for heat, but the furnace is getting to hot, shutting off and then cooling down and reigniting.
This is usually caused by not enough ductwork or a disconnected duct pulling hot air back in to the intake.
Given that yours has changed, I would guess that it was not enough ducts, and one may have split open- or you had a register that was closed that is now open.

Sorry about that- I went and reread your post- it does sound like the relay- I’m assuming that you don’t have one of the newer models with the fan relay on the circuit board.

Steve P- if you have a heat only thermostat , which only works the furnace, you can just take the wires off the thermostat and hook them together- the thermostat is simply an on/off switch.

–Chris

[Reply]

FMB on Thu, 10th Apr 2008 12:29 am


Chris, thanks for the reply. It is a SF30F and I don’t see a relay in the Installation instruction manual diagrams so I’m thinking it might be integral to the circuit board. I will have to pull the furnace out to determin that.

Oh, wow. Am I glad you only struck through and didn’t delete your first comments. I always thought the bathroom floor vent didn’t blow much and the bedroom vent blew less (barely felt air move). I took the cover off to measure voltage on either side of the Hot limit switch and it dawned on me the amount of air blowing with the front cover off was enormous. With the cover off heater on, the blower sends copious amounts of heated air into the room through where the cover and cabinet intake vent would have been. When it came time to turn off, it went through a ~2 min cycle and turned off. I repeated this several times. With the covers on, it cycled 3-5 times. Hmmmm…. plugged vent tubing somewhere I’m guessing now, cause when I remove the vents out of the system, the heater works fine. Back to looking at vent tubing tomorrow. Thanks.

[Reply]

Mike on Wed, 23rd Apr 2008 10:47 am


I have a Suburban furnace in a ‘87 Winnebago.
It worked fine until the day I needed it and then
nothing. Any suggestions where to look first?

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Jami on Wed, 7th May 2008 10:42 pm


I need some help! I have an Atwood Mobile Products Furnace in an 04 Bayhauler Trailer. (Mod # 8520-IV-DCLP) The wall Thermostat control is a Duo-Therm by Dometic. The furnace kicks on, ignites and blows hot air, unfortunately it si for a very short peroid of time. The heater will blow for a few minutes and shut off. The camper never gets warm. The heater has worked fine and now all of the sudden isn’t working right. He have taken the inside and outside cover off and blown air around to see if it could be dirty. Any suggestions?
Thanks- if you can help it would be great it sure is cold in Wyoming!

[Reply]

Rod Wesling on Fri, 9th May 2008 2:58 pm


I have 86 winnie motorhome with Atwood 7912 Hydro Flame,blower(fan)runs continuously when thermostat is turn, on but no ignition(flame),gas is on,would you give me a step by step run down so I can find and correct the problem? Thanks Rod.

[Reply]

Doug H on Tue, 20th May 2008 8:32 pm


Chris: Have a Suburban SF-35F furnace in an 05 Hornet Retreat. Has worked fine for the last 3 years until last weekend. Turned furnace to Heat and instead of the blower coming on and running for 30 seconds to 1 minute before igniting all we got was a buzzing noise coming from the furnace. Turned furnace off and buzzing noise remained until approximately 1-2 minutes before buzzing noise turned off…almost like a blower cycle time. Waited about 30 minutes, turned back on, same buzzing noise occurred. Pulled furnace out, and with switch in heat mode buzzing noise occurred and noticed blower fan moving very slowly. Tried it the next weekend to see if there was any difference, furnace did nothing, no buzzing, no blower, nothing. Any ideas?

[Reply]

Chris on Wed, 21st May 2008 2:02 pm


Hi Doug,
It sounds like either the blower motor or the fan relay. I would hook 12 volt power directly to the blower motor to see if it will run OK (make sure the blower will turn freely, as well).
If the furnace has the outside door, you should be able to do this without pulling the furnace out (IIRC).

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Doug H on Wed, 21st May 2008 5:40 pm


Follow-up: Is the relay inside the furnace by the blower motor? No access door from the outside. Will there be 2 wires on the blower motor that I can hook 12v to, and is the white wire the ground on the furnace also?

[Reply]

nicole on Fri, 23rd May 2008 10:10 pm


i have a wall furnace(no idea what the make is) and it is controlled by a wall thermostat. it started to make a popping sound and than a ball of fire would come out from the grill. turned it off and cleaned it up, called the gas co and they said to let the dust burn. turned it on after it had burned clean and it popped and fire came through again. we have been using it for the past 7 years and never had this occur before. any idea what it could be? thanks

[Reply]

Doug S. on Sun, 1st Jun 2008 10:12 pm


Chris,

I have a Suburban furnace in my 01 Sierra. I have had an ongoing issue with the furnace that is frustrating me big time.

With fully charged batteries my furnace will run 2/3 through the night before it stops igniting and the fan runs cold. Last year my converter went on the fritz and I figured it wasn’t charging the batteries good enough. This year I installed a PD power distro center with the charge wizard. I still get the same result from my furnace. If I plug my truck into the trailer the furnace will run all night but if it runs off my batteries alone it will stop 2/3 through the night. I have two deep cycle batteries that load test really well and through all this the lights in my trailer never go dim so batteries are not on my list.

What is going on??

I replaced the blower motor

[Reply]

Doug S. on Sun, 1st Jun 2008 10:15 pm


Continued:

I replaced the motor in my furnace, it was dirty and the bearings were rough. I figured this was my issue but it is not.

[Reply]

Chris on Mon, 2nd Jun 2008 8:33 am


Hi Doug,
I would bet that there is a voltage drop somewhere in the system- probably several, so even when the batteries are still up, the voltage to the circuit board gets low enough that it will not operate correctly.
*If* the wall thermostat only works the furnace (and not the rooftop air conditioner), I would start there, but I’ve seen a lot of limit switches (which you access by removing the inside cover) with enough oxidation to severly drop the voltage- as well as the sail switch.

[Reply]

Doug S. on Mon, 2nd Jun 2008 8:54 pm


My thermostat does control the rooftop A/C and the furnace. So I start by inspecting the limit switch(inside the furnace) and then the sail switch. What would the normal voltage drop across these components be?

Is it safe to say seeing how the system works with the truck hooked up that the circuit board is OK?

[Reply]

Doug S. on Mon, 2nd Jun 2008 8:58 pm


My thermostat does control the rooftop A/C as well. I guess I will test the sail switch and the limit switch for voltage drops, what would you say is maximum acceptable across both these components?

Is it safe to say my circuit board is operational with no issues or may I have an issue there?

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Anonymous on Thu, 24th Jul 2008 12:35 pm


i have a lennox system that the blower motor is staying on i chesck the limit swiths for conunity they r all fine i think it is the circuit board what do u think

[Reply]

kathie cooper on Thu, 31st Jul 2008 7:03 pm


i have an bryant gas furnace it was working fine on a summer eve.i had the a.c. on with the thermostat set on auto. I switched it to off,and also switched it to fan but the fan would not work. I tride a.c. with fan an d with auto. i also tride heat with fan and with auto. a.c unit out side turned on but no forced air.furnace turnd on but no forced air wat is the problem.

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Christine on Wed, 20th Aug 2008 1:59 pm


Having problem with my Duo therm Dometic Unit The ac will not cut off by itself when it reaches a certain degree you have to cut it off by the hi lo switch. It will not cut off with the Heat off Cool switch. I have replaced the thermostat, control board, and a compaster on top. Have checked wires need help I don’t know what else to check. please email me. Thanks

[Reply]

Chris on Wed, 20th Aug 2008 5:10 pm


Hi Christine,
It sounds like you have replaced everything I would check, but it is very possible that you got a bad (or wrong) thermostat. Dometic has many different thermostat/control box versions.
Can you give any more information, like a part number for the circuit board or thermostat you installed?

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Christine on Wed, 20th Aug 2008 5:37 pm


I’m at work right now but I get off at 8 tonight I took the old one with me and got the same kind . Thank you for writting me back. I can;t thank you enough. I will write you back as soon as I get home Also it is doing the same things the other thermostat was doing. How it has been working On the thermostat there is heat off cool hi lo on auto. It use to cut off when it got a certain temp like if it is set on 70 it would cut off but know it will not. the fan goes from high to low fan and the only way you can cut it off is by switching it to lo with the hi lo switch. It will not cut off with the heat and cool switch when you cut it to off it cuts the fan on low. It was working fine till one night I was alseep and heard a pop and got up and heard the fan on low and every since then it hasen’t worked right. Thank you for your help.

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Christine on Wed, 20th Aug 2008 6:11 pm


Here aresome numbers I had wrotten down 3104757.004 control board 3104998 board and thermostat Relay kit serial #E6147786 for use with 579, 590, 595, 600 series Model 57915.421 Duo Therm Model 57915.421 product 991731645 Serial 61616390 Hopefully these will help.

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Chris on Thu, 21st Aug 2008 5:11 pm


Many apologies- I’m just not going to have time to research this right now, either here or on my RV.Net blog,as my shop and house are under water from TS Fay (and I only have about 1 hour of power per 6).
Arghh…. about 15-20 inches of rain in the past 8 hours, with more to come :(.

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Christine on Fri, 22nd Aug 2008 1:03 pm


sorry to hear that hope things get better. I will keep you in my prayers.

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Dwayne on Sun, 21st Sep 2008 7:03 pm


Hello Chris -
First: Hope your home is ok after the flooding!
Second: Thanks for a great resource & the personal responses for all here.

Here’s hoping I can contribute something for those of us with older RV’s.

Hunter 40020A mechanical thermostat sells for $10.20 at Lowes & is a generic replacement for the HEAT ONLY systems like my old camper’s Duo-Therm 65900 heat only furnace.

Manuals for many furnaces & RV appliances can be found at

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Dwayne on Sun, 21st Sep 2008 7:05 pm


Manual link didn’t show up so here it is again:

http://www.bryantrv.com/owners.html

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cameron on Sun, 21st Sep 2008 11:52 pm


I have a furnace not sure of the brand but sometimes it won`t ignite or it will after trying many times do you know what it could be?

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cameron on Sun, 21st Sep 2008 11:53 pm


by the way its a rv furnace in a 1982 23ft prowler

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Tom on Tue, 23rd Sep 2008 6:30 am


RV furnace will run 1 good cycle. On the second cycle,the blower comes on but no heat just cold air out the ducts. Need help please

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larry on Tue, 30th Sep 2008 2:46 am


i live in a 1973 double wide mobile home. it has a Coleman cool and heat furnace we replaced the blower moter, everything seams to work good now but the the transformer makes a humming noise all the time. my question is, is it normal for the humming or is the transformer no good, etc.

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Scott on Sun, 12th Oct 2008 10:04 pm


Hey Chris,
I have a Rockwood pop-up with a Suburban DD-17DSI, I need to replace the thermostat but don’t know what to set the anticipator to. What does the anticipator do? If set wrong what could happen?
-Scott

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Chris on Mon, 13th Oct 2008 5:00 pm


Hi Scott,
The anticipator actually provides a very small amount of heat directly to the thermostat- so that the furnace will shut down just a bit before the set temperature is reached (because the furnace runs for a while blowing off residual heat) so that it will not get too hot.

That said- the anticipator should be set at .7 for Suburban furnaces (1.0 for Atwood/Hydroflame)- a common mistake is to set it too far down (to .2 or .3) which will burn it out from too much heat.

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travis j. on Wed, 22nd Oct 2008 9:20 pm


I have a Suburban furnace in my travel trailer and when i turn it on, after about 20 seconds the fan turns on an blows cols air and nothing els happens, but it is getting fuel though.

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Tommy on Fri, 7th Nov 2008 4:14 pm


I have a lennox propane furnace, it will light for a few seconds, then go out, re ignite, burn for a few seconds and go out….. have replaced regulator at tank did not fix, replaced line with new one, did not fix, what is left? Someone told me it sounded like water in propane tank. What does everyone think problem could be?

Thanks,
Tommy

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Chris Reply:
November 9th, 2008 at 6:15 pm

Hi Tommy,
I’m afraid I don’t have any knowledge of home style furnaces, but it sounds like one of two problems- either fuel (which you have dealt with partially), or the flame sensing not working.
Home style furnaces use a lot of different methods to sense the flame, but I just don’t know about them.
Sorry…

Brenda Brooks on Thu, 13th Nov 2008 9:41 pm


Hi, I have a Suburban furnace in my camper. when i turn it on it runs great for a while then the blower starts turning off and on at 2-5 second intervals. Do u have any idea what could be wrong? its getting cold =(

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Flip on Fri, 14th Nov 2008 7:04 pm


I have a Suburban furnace in my RV. It fires and runs fine until it hits the set temperature. It then will not relight. The blower goes, and it sparks, but no gas. Anyone seen this before?

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Chris M on Sat, 22nd Nov 2008 11:36 pm


I have a similar problem Flip. I also have a Suburban furnace in my 89 travelmaster that does the same thing. Usually only in the middle of the night when everyone is asleep. Lost of good info in this thread though. I’m going to go out and start checking voltages.

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Hammer on Wed, 26th Nov 2008 7:23 pm


I have a 2006 cougar with a subarn furnace want come on with remote or by pushing heat butt no nothing what do i do

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robert lequier on Thu, 27th Nov 2008 11:07 am


i have Coleman furnace ,when i light the pilot,it lights okay,but when i let up
the switch to turn it on the pilot goes out.. i have got it started a couple of times
the furnace has lit ,but after it cycled the pilot was off again

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ty Reply:
December 2nd, 2008 at 10:02 pm

sounds like the thermocoupler

Ty on Tue, 2nd Dec 2008 10:14 pm


i have a Suburban sf35 in a 92 bounder. turn it on ,blower starts up,you can hear the igniter clicking………..no ignition. the clicker comes on several times. no ignition. plenty of propane in the system. took apart unit ,checked the orafice.looked good cleaned it anyway,replaced,no change…..-any ideas???????????????????

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Anonymous on Wed, 3rd Dec 2008 2:09 am


WHY DOES A FURNACE IGNITER STAY LIT CONTINUOUSLY?

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Anonymous on Wed, 3rd Dec 2008 2:12 am


OH! ALAN

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Alan on Wed, 3rd Dec 2008 2:28 am


Sometimes soot can get into pipes and cause the furnace to go off and on without reaching the right temperture.

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Don Mckernandoss on Fri, 12th Dec 2008 12:36 pm


Alan… I have DuoTherm ac with surban furnace. New thermostat… now the furnace won’t shut off until I disconnect all power.
I disconected the red wire at the thermostat but the furnace
just keeps on going.
I doublechecked the wiring at the thermostat and it’s correct to mfg spec.
Any ideas?
Thanks, Don

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Chris Reply:
December 14th, 2008 at 8:30 am

Hi Don,
I’m assuming you have a DuoTherm Analog wall thermostat- with a slider to set the temperature. On that setup, the furnace is actually controlled by the circuit board in the ceiling assembly, and is hooked to the blue wires with a white stripe. At the thermostat, the white wire is the furnace lead.

Gordon on Sat, 13th Dec 2008 12:03 pm


I have a Suburban sf35f, year 2005
weird findings
will not fire at 13.6 volts
put a batt charger on at 12 v and it fires, drops to 10.8 v and runs fine
fires every time
Gord

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Chris Reply:
December 14th, 2008 at 8:32 am

Hi Gordon- that is odd. I would be tempted to look at the grounding (I always look at the grounding!), but it could just be a bad circuit board.

Anonymous on Sat, 13th Dec 2008 9:40 pm


I have a 1977 Traveleze Trailer. It has a Duo Therm Furnace. The pilot lights, But when we turn on the blower the burners turns on, then a minute later the burners shut off and so does the pilot. What could be the problem

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Chris Reply:
December 14th, 2008 at 8:34 am

Most of the time that’s a cleaning issue- the pilot is not burning correctly, and when the blower comes on, it pulls the pilot flame away from the thermocouple, so it then shuts down.
Because of the age of that furnace, it really needs to be pulled, inspected and cleaned to make sure the combustion chamber is solid, and all gaskets are good.

Sammy Andrews on Sun, 14th Dec 2008 12:08 pm


My friend called me and asked if I could help out with this problem. The only problem was is that I dont know how furnaces really work. He said that he can turn the heat on but it just blows air out not heat. What would be the first thing to check out frist? The theromstat,pressure switch or would there be another route you would take?

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david on Sun, 14th Dec 2008 3:36 pm


my furnance just started acting up. theres a red light that flashes six times which tells me that the pressure switch has shut down. also ever since i ahve removed the face panel from the furnace it run great but when i replace the face panel. the furnance wont run properly…..what is going on?????

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Chris Reply:
December 18th, 2008 at 2:29 pm

Hi David,
A couple of things come to mind- there is an air prover (a.k.a. sail switch) right inside the outer plastic blower housing. It sounds like this is either bad, or the return air is blocked somewhat, or the voltage is low and the motor isn’t turning quite fast enough.

Sammy Andrews on Sun, 14th Dec 2008 9:48 pm


I think its a duncan it had a ignition switch that said off and on. down where the burners where it was not getting anything. I took pictures. I also changed out the thermostat and it still did the same thing. i turned it on and the fan and blower came on but no heat. Please help.

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Cold in Nevada on Wed, 17th Dec 2008 9:48 am


We have a Suburban SF 25F, last night it blew cold air long enough to get to 45 in the camper and wake me up - it was 8 outside. I turned off the furnace for a while, then turned it back on, it blew warm air for about 15 minutes, then the air turned cold again. Any help or suggestions would be great…thanks!

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Pat in Nevada Reply:
December 18th, 2008 at 2:19 pm

Where in Nevada? We are in Dayton, NV Having trouble with our heater, too, and we installed it NEW last Dec., fan but no flame. Already replaced the igniter, twice!
But this time it isn’t fixing the problem. Further troubleshooting needed. Temps near 0 now. Sure can’t afford to buy another new heater @ $700.00 Any suggestions out there????????



Chris Reply:
December 18th, 2008 at 2:32 pm

On that model I have found the limit switch is the most failure prone part- you can easily get to it from inside the rig- there will be n access panel (the whole inside panel) that is held on by a couple of screws, and the limit switch is right behind it- it’s a small oval switch with two wires leading to it.
Often simply disconnecting and reconnecting the wires will fix it for a while.

Patricia on Thu, 18th Dec 2008 2:10 pm


We live in a 1979 35ft Komfort fifth wheel and had a Suburban NT30SP, which we had to replace exactly one year ago with a supposedly NEW one (from an RV supplier), same model. We have already replaced the igniter a month ago, and now the furnace is doing the same thing again. We bought an extra igniter last month, but that isn’t working. Still have the same problem, fan but no flame. Are we going to have to go throught this every winter? We lived in the RV for 10 years before we had to replace the heater. And with the new heater, seems as though we may have a lemon. Any recourse with that?

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Chris Reply:
December 18th, 2008 at 2:37 pm

Hi Patricia,
That really isn’t normal- really the only design problem I see with the NT series is that the circuit board is too close to the combustion chamber- Dinosaur makes a board extender which will move the circuit board outside the case, which both keeps it cooler and makes it much easier to troubleshoot.
That said- I would closely look at the installation- especially supply and return air flow, as well as trying to bypass the thermostat to test.



Pat ricia Reply:
December 18th, 2008 at 3:22 pm

Already bypassed thermostat. Heater was working fine this morning at 6:30 when we turned thermostat up (we turn it lower at night). But by 7:00 it was no longer igniting.

Pat on Thu, 25th Dec 2008 10:45 pm


I have a Suburban NT30sp when I turn it on and adjust the thermostat to a high temp, the blower comes on , but the burners do not light and I can’t hear the igniter sparking, want could be the problem

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george on Fri, 26th Dec 2008 8:08 pm


My old duo-therm just stopped lighting up, the blower comes on but no heat. I replaced the controller board with a 50 plus board. Now the blower comes “ON”, I hear the igniter and smell the gas coming out the exhaust, but it just won’t light up. I have tried adjusting the air shutter, but it just won’t light. Any ideas?

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Bill Zimmerman on Sun, 28th Dec 2008 1:56 pm


1st, thank you for what you are doing here!

I have an 06 Laredo with a Suburban NT-30SP heater and a Colman Mach thermastat (Air & heat)

I have had the unit in shop several times for this problem, but they could not resolve.

Problem: Heater comes on, heats, cools down, turns off and then immeditaly turns back on. It will stay on for several minutes, (No heat) turn off, and again immeditaly turn back on. This cycle continues untill I turn off at thermastat.

I need to use this unit this week for additional rooms as family is staying for wedding.

Thanks again for this,
Bill Z

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Bill on Sun, 28th Dec 2008 6:04 pm


Chris,

I have a 1976 Winnebago Brave. My furnace won’t stay lit, but when I relight the pilot, it stays on until I turn the furnace on, then the pilot goes out. I have changed the tanks and regulator and hoses, and now the pilot won’t stay lit. I bought a thermocouple, but don’t know how to change it. Any tips, and do you think that is the problem?

Thanks,

Bill

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shelia d. hobbs on Wed, 7th Jan 2009 2:26 pm


I would like to know why my furnace blows cold air after running for a while, it doesnt do this all the time but every once in a while it starts to blow cold air and I have to turn it off and re-set it.

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Anonymous on Thu, 8th Jan 2009 9:54 am


Why does my furnace click on for 3 seconds then clicks off, then back on again and stays on till it reaches temperture?

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