Furnace won't shut off...

monkey · 05-11-2012, 01:00 PM

I am having a problem with my furnace, it won`t shut off when the selected temperature is reached on the thermostat. Only when I slide the temp selector all the way down or if I select the switch to off will it shut off. I had the same problem beginning of last season and I replaced the thermostat and it worked fine all season untill I tried it recently. The new thermostat was put in in June of last year, it`s a dometic one that controls the furnace and AC. I would think that it should last longer than 11 months, especially when it was only used from June to September.

Does anyone have any ideas to help, The furnace is a SF30F and the camper is a 2006 Springdale 298BHL.

Thanks

f6bits · 05-11-2012, 01:16 PM

That sure sounds like a thermostat issue. Is that one of their digital thermostats? If not, replace it with a home digital thermostat. They’re *so* much nicer! And seeing how yours is out of warranty, I’d still recommend a Hunter or Honeywell thermostat even if your Dometic is digital.
http://www.modmyrv.com/2008/07/14/rv-digital-thermostat

EDIT: Ok, I’m not a close reader. Yours is old-style slider type. Ditch it and go Digit…ul (it sounds better out loud).

SteveC7010 · 05-11-2012, 01:41 PM

Quote:

Originally Posted by sdayman

That sure sounds like a thermostat issue. Is that one of their digital thermostats? If not, replace it with a home digital thermostat. They’re *so* much nicer! And seeing how yours is out of warranty, I’d still recommend a Hunter or Honeywell thermostat even if your Dometic is digital.
http://www.modmyrv.com/2008/07/14/rv-digital-thermostat

Fully agree!

The Dometic old style thermostats are very unreliable plus they are expensive to replace. When the one in my previous trailer started to act just like monkey's, the RV stores all wanted about $55 for a replacement. The Hunter 49995 was $22 at Wal-Mart at the time.

The Hunter is much more reliable and accurate. They do need a pair of AA batteries, but like the smoke and CO detectors, you replace them all annually any way.

The swap instructions from modmyrv are very straightforward and easy to follow.

Go for it.

monkey · 05-13-2012, 07:52 AM

Thanks for the quick responses guys. I live in Newfoundland, Canada, and I can't seem to find the Hunter Digital Thermostats on any of the store websites (Walmart, Home Depot etc) in my area. Are there any other thermostats that will work. Honeywell seems to be the most popular in the stores here.

What would I need to look for when looking for one?

f6bits · 05-13-2012, 08:10 AM

I use a Honeywell $20 thermostat. Just about any home thermostat works. As long as it has the typical controls: Fan: On/Auto, Cool/Off/Heat, and Up/Down temperature, you’ll be fine. It *has* to require batteries since you can’t use the trailer as a power source.

I use this one:
http://www.amazon.com/Honeywell-RTH1.../dp/B000WEOQ6I

You can certainly use the fancier programmable/touchscreen ones.

monkey · 05-13-2012, 12:23 PM

Thanks again, I'll look into that one. For now I got a dometic one from a friend that he had as a spare. Furnace works fine again. What is causing the thermostat to crap out. Is it really a crappy thermostat, or is something in the AC or furnace system doing it.

chain_dogg · 05-14-2012, 01:53 PM

My trailer turned out to be a sail switch gone bad........same proplem

SteveC7010 · 05-14-2012, 02:55 PM

Quote:

Originally Posted by monkey

Thanks again, I'll look into that one. For now I got a dometic one from a friend that he had as a spare. Furnace works fine again. What is causing the thermostat to crap out. Is it really a crappy thermostat, or is something in the AC or furnace system doing it.

The Dometic is dependent on a crappy thermistor and cheap slide switch for the temp sensing and set point respectively. Neither are particularly accurate. The slide switch usually goes first and almost anything can cause it. It's just a piece of junk.

No matter what trailer manufacturer you look at, all the users have troubles with the Dometic thermostats. You'd think Dometic would get the hint.

Davkar · 12-02-2019, 07:09 PM

Quote:

Originally Posted by monkey

I am having a problem with my furnace, it won`t shut off when the selected temperature is reached on the thermostat. Only when I slide the temp selector all the way down or if I select the switch to off will it shut off. I had the same problem beginning of last season and I replaced the thermostat and it worked fine all season untill I tried it recently. The new thermostat was put in in June of last year, it`s a dometic one that controls the furnace and AC. I would think that it should last longer than 11 months, especially when it was only used from June to September.

Does anyone have any ideas to help, The furnace is a SF30F and the camper is a 2006 Springdale 298BHL.

Thanks

I was having a similar issue on a Suburban Furnace where the motor was staying on when the heat had reached the desired level. I discovered my thermostat was sending a signal of some kind to my AC about 10 seconds before the one to the furnace and the AC was making a clicking noise for those 10 seconds like it was trying to switch on. I saw that the AC was set to 70F and the furnace to 71F and thought the 2 numbers were perhaps too close to each other. I switched the AC to 80F and so far this seems to work, I assume because the thermostat now sends to the furnace first.
If this is not the case at least I know the issue is with the thermostat (easy to replace) rather than the control module (would have to remove the furnace to get at it).

**flybouy** · 12-03-2019, 06:02 AM

Quote:

Originally Posted by Davkar

I was having a similar issue on a Suburban Furnace where the motor was staying on when the heat had reached the desired level. I discovered my thermostat was sending a signal of some kind to my AC about 10 seconds before the one to the furnace and the AC was making a clicking noise for those 10 seconds like it was trying to switch on. I saw that the AC was set to 70F and the furnace to 71F and thought the 2 numbers were perhaps too close to each other. I switched the AC to 80F and so far this seems to work, I assume because the thermostat now sends to the furnace first.
If this is not the case at least I know the issue is with the thermostat (easy to replace) rather than the control module (would have to remove the furnace to get at it).

A 1 deg differential is too narrow for any t'stat in my opinion. I don't know if this causing your issue or not. I'd try a 4 deg separation and see how that works.

Archergodwin · 12-08-2019, 05:54 AM

I installed a 7 day programmable Filtrete thermostat several years ago. 3AA batteries would last almost a year. Ran the living area A/C and furnace great. I think it was 30 bucks or so at HD.

I have since gone to Dometic Zone control using the CCC thermostats (big project).

Davkar · 12-08-2019, 08:34 AM

I bought a cheap $33 programmable one but the wiring colours and voltage didn't match and even though the new one used batteries I didn't want to risk damaging something so I thought I'd give the Dometic one another chance at redemption.

I re-initialised it (plus sign and off button for 3 seconds)
I made sure AC temp was 10 degrees above furnace
Verified temp differential was default 2 degrees - not 1

#1 and #3 fixed the motor run on issue
#2 fixed the AC clicking noise

All is working now and I returned the $33 one. If the voltage difference 12V versus 24V doesn't matter if it used batteries please let me know because I liked the programmable option on the cheap thermostat.

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