Furnace operation question

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Lowell

Lowell

Well-known member
Joined
Aug 15, 2005
Posts
2,221
Location
Tempe, AZ
We were camping this past weekend at 9000 ft and it got down to 28 degrees at night.  Although we didn't use the furnace much, we did use it to take the chill off. On the last afternoon and evening, I turned the furnace on for bit and got a little warm so I turned the thermostat down and in a short bit the furnace shut down as expected.  Later that evening, it didn't come back on and I turned the thermostat up higher and higher and it still didn't come on. I turned the furnace switch off and back on again a few times and still no luck so I shut it off and left it.  A couple of hours later before going to bed I decided to try it again and it started right up and continued to operate correctly all evening.

I wondered if anyone had an idea why I had the problem? Is there an overheat switch or breaker that might have reset itself?
 
I would suspect the thermostat and/or the thermostat sensor before anything in the heater itself.  We had a fifthwheel that had the temperature sensor right over one of the floor vents.  That didn't work well until we blocked off that vent.
 
Several years ago, one of the neighbors had the service guy out to check out why the furnace wasn't working.    He removed the rugs off of the heater vents.  Everything worked fine then.  Don't know how many vents can be covered before the furnace won't work.


Wi1dBi11
 
Wi1dBill said:
Several years ago, one of the neighbors had the service guy out to check out why the furnace wasn't working.    He removed the rugs off of the heater vents.  Everything worked fine then.  Don't know how many vents can be covered before the furnace won't work.


Wi1dBi11
Click to expand...
The high limit switch failed on our S&B furnace. The tech asked if we keep some vents closed. When I said we did, he told me that restricted airflow will cause the high limit switch to overwork itself. Make sure you have enough vents open and no blockage of the cold air intake.
 
The odds of the high-limit switch failing are slim but not zero. However, the high limit switch doesn't even come into play unless the fan runs and the ignition sequence starts.

I can't tell from your description whether the furnace tried to light and failed, or simply didn't try. If the fan came on, it is trying. If not, then either the furnace has no 12v power or the thermostat isn't sending the "heat needed" signal (+12v on a wire to the furnace control board).

You may get some useful help from my Library article on Furnace Troubleshooting: http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf
 
Normal furnace operation when the Thermostat calls for heat the blower should fire right up The burner fires up a bit later.. If the blower did not start.. I support the T-Stat as the problem.
 
    Gary, you are probably correct. I was thinking that if the switch "showed high temp" then it would prevent the "start cycle" from occurring. I know in industry...you can't start equipment until all "trips" are cleared/reset.
 
Thanks for the replies.  No, the blower didn't come on. So I'm guessing it must have been a thermostat issue?
 
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