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Old 09-25-2016, 08:51 AM   #1
Jim M
2012 23' FB International
Durango , Colorado
Join Date: Feb 2012
Posts: 11
furnace not working

When i turn on thermostat furnace blower blows out cold air for about 3-4 minutes and then stops. Two months ago, when I last used furnace, I noticed that the mode display of the dometic thermostat read a nonsense word instead of "auto" but it still worked fine. It still shows the same nonsense' but doesn't work as I first mentioned. Any suggestions? Thermostat problem or furnace problem?

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Old 09-25-2016, 09:07 AM   #2
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2016 28' Pendleton
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Scottsdale , Arizona
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Hi from AZ. . . your problem is. . . the warranty just ran out ! Amazing how the furnace knew that, eh ? Seriously, I always check myself with the easy stuff first. . . propane is ON, propane tank is NOT empty, stove top lights (i.e. line not airlocked), no blown fuses. just thinking out loud here. . . good luck, Craig

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Old 09-25-2016, 09:38 AM   #3
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2002 30' Classic S/O
Melbourne Beach , Florida
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I would say that since the furnace blower runs, the thermostat is OK. After you check the obvious items listed by RamblinMan, there is a "sail switch" in the airflow inside the furnace. If the airflow doesn't actuate it due to it being stuck or defective, the gas doesn't turn on. If the gas doesn't turn on and the furnace doesn't heat up, another safety mechanism turns the blower off. I've never had this problem, but search on here for furnace sail switch or other furnace won't light threads and you should find something that shows you where it is and how to check it.


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Old 09-25-2016, 05:47 PM   #4
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2003 22' International
South Bend , Indiana
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Shine a flashlight into the exhaust pipe and make sure it isn't plugged with mudauber nest.

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Old 09-25-2016, 05:58 PM   #5
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2014 23' FB Flying Cloud
Park City , Utah
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Checking the 'sail switch' is a good place to start, assuming propane is flowing to other appliances. It is inside the furnace cover on the exterior. If it's stuck, the moving air won't open it, allowing gas to flow.

As for the thermostat readout, I had exact same problem last year on a 2013 Flying Cloud. Except my garbled readout was in the setting that should have read "Furn". Didn't impact operation, though.

I emailed Dometic and they sent me the following instructions to reboot the thermostat and hopefully fix the problem. I never did get around to trying it, but here they are:

'Thank you for contacting Dometic. To do a system initialization, or a "reboot" or your thermostat, first turn it "off" (it will either have a blank display or show only the clock) At the same time, hold the Mode and Zone buttons. The screen will display "IniT" and all available zones. When that happens, release the Mode and Zone buttons and turn your thermostat back on. Sometimes, you need to do this a few times before your thermostat "finds" everything it's going to run. Hopefully, that should correct the gobbledygook that you're getting.'
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