Furnace forgets to come on

[Invizatu]

Not all the time of course, that would be easier to figure out.
Furnace will be run fine, come on and go off several through several cycles and then it will "forget" to come on when temp drops below
the set point (3 degrees or more).
Any suggestions
Thanks... Bret

 

[danemayer]

Hi Bret,

How are you checking that the temp is 3 degrees below the set point?

Does the furnace come back on if you raise the set point, or do you have to cycle it off and back on?

 

[mikesmith5984]

I have something close to this problem your having mine does come on but then shuts off if I keep turning it on and off it will work have not got it figured out yet


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[Invizatu]

Hi Dan

Going by what the thermostat reads ( I have an extra thermostat that I have swapped out & does same thing )
Have to turn off and back on.

Thanks

 

[danemayer]

If you have to recycle it, that usually means it's going into a safety lockout because there were 3 ignition attempts that failed.

The blower runs for 25 seconds and if the sail switch activates, the gas valve is opened an a spark is generated. You might notice a short furnace cycle - maybe a minute or so and then later notice that it's getting cold inside.

Low propane flow is the #1 cause. Could also be low voltage from the Battery/Power Converter. Blockages in the vents. Bad circuit board. Bad gas valve - but that's low odds.

 

[Invizatu]

Fan does not even come on.
Does not happen very often, but of course it will be around 3:30 am! lol

Replaced propane regulator today and it ignites every time now. (This was obviously a different issue / solved)

 

[Invizatu]

Hi Dan... It will also not shut down when it's supposed too. Thermostat set at 70 and temp inside is 76! Drop it a degree and then it shuts down.
It's driving me nuts!

 

[avvidclif]

Look at the placement of the thermostat in the RV. They stick them wherever, not necessarily the best place. Mine in the living area are over 6' high. Makes for a hot head and cold feet. That's why we have fans going, to circulate the air.

Is the thermostat and the temperature gauge at the same spot and height? Across the room and higher or lower doesn't count.

 

[danemayer]

Hi Dan... It will also not shut down when it's supposed too. Thermostat set at 70 and temp inside is 76! Drop it a degree and then it shuts down.
It's driving me nuts!

Bret,

The gas regulator problem might have explained the problem where it doesn't come on and goes into lockout mode. But it sounds like you've replaced the regulator and still have that symptom.

Both the doesn't start and the doesn't stop could be caused by the thermostat, but if you've replaced it, the next part in line is the relay that the thermostat operates. It's usually located in a box above the Air Conditioner return - if you have Whisper Quiet, it may still be on the underside of the living room AC unit, even if there's no return there.

Could also be a problem with the furnace control board or its wiring having a poor connection, or with the gas valve not opening and closing reliably.

I think I'd check out wire nuts and connections on the control board before replacing parts.

 

[Invizatu]

Thanks Dan, process of elimination!