Comments on: Furnace Troubleshooting (the first step)

By: Paul

Paul — Sat, 03 Jul 2010 15:57:45 +0000

Hello Chris,

I have just purchased a 77 country camper with a suburban furnace. Everything worked except the Suburban NT furnace. I took it out and found burnt ground wires had them replaced and Bench tested its good to go now except when I reconnected it, wires were getting hot and blew fuse. I think that might have been original problem and re wired it all is good now except fan stays on when thermostat is off.. This is a heat only setup, do you think I need new thermostat? also when I turn sterio on fan runs faster and interior lights get brighter??? Scary

By: Cory

Cory — Tue, 08 Jun 2010 00:36:18 +0000

I have a similar problem as jim i have a suburban furnace in my palomino and I recently replaced the duotherm analog thermostat with a Honeywell RTH7600D digital thermostat and the furnace runs great for many hours until the blower starts for 2 seconds then goes into lockout mode and will not turn on again until the thermostat is switched off and then back on. I figured it was the thermostat but after I have tried 3 different ones and it still does the same thing im not so sure. I then installed the duotherm back in and it ran 2 days in a row fine so I put the honeywell back in and same thing after 6 hours of cycling on and off fine it decides to stop running the furnace and I wake up and its 4 degrees inside my rig. The thermostat will say heat on in the lcd screen meaning the furnace should be running but its not. And when it has done this i pulled the fuse to the furnace to see what actually needed to be reset everytime the furnace or the thermostat so when the furnace quit working i left the thermostat where is was pulled the fuse to the furnace and reinstalled and the furnaced kicked on immediately! Im completely confused with whats going on any idea?

By: Jim Scheel

Jim Scheel — Fri, 28 May 2010 14:54:44 +0000

I have an Atwood 8535 IV furnace in our RV. Intermittently (probably about once in every 10-20 starts) it will not start. When the thermostat calls for heat nothing happens. The fan does not start, the furnace does not fire. Upon removing the outside cover, the error code light indicates “Limit switch/Air flow problems”. After trial and error I found a way to get it to run again: push the reset switch which removes the error code light, and give the squirrel cage fan a flip with my finger. It instantly starts and the furnace cycles normally. Everything is fine until the next intermittent time it will not start. I’ve had it into an RV service center and of course it operated perfectly. One comment the tech had was it may be low voltage but we were plugged into 50 amp shore power during the time it malfunctioned. Any ideas?

By: Ralph

Ralph — Thu, 27 May 2010 18:53:56 +0000

i have a wall furnace who’s pilot is still lit but wont go on. replaced thermostat and still won’t work. please help.

By: Melissa

Melissa — Tue, 25 May 2010 00:59:05 +0000

I have a Suburban NT Series furnace which lights up normally and heats for about 5-7 minutes then the heat starts going away until cold, but the blower continues and doesn’t shut down until i turn it off.

What is the solution?

By: patricia whitford

patricia whitford — Sat, 22 May 2010 19:52:42 +0000

sorry I just gave y0u the wrong email address see above is correct

By: patricianwhitford

patricianwhitford — Sat, 22 May 2010 19:51:39 +0000

I have a sf 30 suburban gas furance and it blows cold air we tryed to chage the limit shitch but tha never helped we can hear the electroic switch trying to igniote ut no heat comes through can you tell me what i need to change ow could it be the theromsate??? or is it something with the ignioter nthanks Pat

By: Bonner Martin

Bonner Martin — Mon, 17 May 2010 09:16:06 +0000

I’m from New Zealand and are having a little problem with my Suburban NT 30 SP heater. It’s run great for 18 years, and has just begun giving problem when starting.

I have followed Chris excellent instructions at the beginning of this blog. And recorded 1.4amps when first switched on by putting an amp meter across the thermostat connections, which dropped quickly to .37 of an amp. Once the fan started the current reading dropped .2 amp with the bulk of the current (6 amps) being carried on the main heater feed. Once the ignition started the current reading dropped to near nothing while the ignition was running. Returns to 6 amps once the ignition stops. There is no loss of fan speed while ignition is running

My problem is that the spark is erratic. Sometimes it is there, other times only one or 2 sparks will occur, sometimes it misses about every 10th sparks. In the clear tube besides the coil one can see sparks between the parallel electrodes.

I have checked all wires for continuity, cleaned all contacts, cleared out the inside of the furnace checked that the dual gas valves are working. Checked the gap on the igniter, it has a more consistent spark with a gap of 3/32 than at 1/8 inches. Checked the printed circuit board for dry joints.

Has anybody got any suggestion. Advise sure would be appreciated and what is the idea of having a neon type display besides the coil. i.e. that the clear tube with 2 parallel rods inside that have discharge between them when the spark is running.

Thank you. Bonner Martin

By: Tom

Tom — Tue, 11 May 2010 12:29:34 +0000

Hi
I have a Suburban SF30F furnace in my Outback that runs intermittently. We can turn the thermostat on, it seems fine for an entire day, then at some point the trailer cools down, the thermostat calls for heat and nothing happens. If it turn the themostat off then on – I can hear a click, but no fan and no ignition. Any suggestions?
Thanks!

By: Al White Jr

Al White Jr — Sun, 09 May 2010 14:17:39 +0000

I just bought a 1994 coachmen catalina, pretty nice camper. The family and i decided to do some backyard camping on the first night, so I hooked up the propane the furnace fired but won’t shut off, even when the thermostat is in the off position the fan continues to blow. the only way to stop the furnace blower is to pull the fuse. I pulled the thermostat off moved the anticipator up and down with no change. I pulled the whole thermostat off and there was ants fried to the cicuits took them off and the same thing. do i start with a new thermostat? or is it something with the furnace. the thermostat will turn the a/c on and off and to high and low but the furnace always stays on. Any help is appreciated. I guess I should mention that it is a suburban furnace with a coleman thermostat not sure on the ac unit though. Also will a house thermostat work for the RV as I can get one of them easier than the 100 mile trip to an rv dealer. Thanks for your help. Al White Jr