Thermostat or furnace problem

[Dick in Wisconsin]

Had a new natural gas forced air furnace installed last fall. Installer hooked it to our existing LUX programmable thermostat; thermostat is probably seven or eight years old.

Twice in the last two weeks I've noticed that the house is cold. I check the thermostat. Its set to 74*F, the temp is 68*F, and the furnace is not running (I have the blower set to run all the time).

So I go to the basement, blower is blowing (like it should), but no fire from the burner. I turn the switch off on the furnace and the blower shuts off. I wait a full 30 seconds. Turn the switch back on, blower comes on, burner doesn't light.

Then I go to the thermostat upstairs. Turn the three position switch from HEAT to OFF. Wait a full 30 seconds. Turn it back from OFF to HEAT. I hear the thermostat click.

Back down to the furnace in the basement and by the time I get to it, the burner is light, lots of fire where it should be, fan is running, furnace is heating.

I don't think the problem is with the furnace. I think the problem is with the thermostat.

Edit: Furnace is a Bryant 925TA48080E17.

What do the experts on the forum think?

 

[brewchief]

Brand and model of furnace?

Should be a blinking LED for trouble codes, is it showing any codes? If so what are they for?

LUX stats are a pretty cheap brand, I wouldn't be shocked if that was the problem.

 

[Dick in Wisconsin]

Brand and model of furnace?

Should be a blinking LED for trouble codes, is it showing any codes? If so what are they for?

LUX stats are a pretty cheap brand, I wouldn't be shocked if that was the problem.

Added the brand and model.

I checked the furnace and the LED is steady, which means "no problem". Next time the problem presents itself, I will check the LED first.

 

[cort]

Do you have a volt meter? Maybe next time this happens, check and see if the thermostat is calling for heat. Check for VAC across W1 and common at thermostat connections in the furnace. If there is 24VAC across white and common, then the problem is not likely the stat. Be advised that you may have to trip a door switch so the furnace doesn't think the front panel has been removed.

 

[Dick in Wisconsin]

Do you have a volt meter? Maybe next time this happens, check and see if the thermostat is calling for heat. Check for VAC across W1 and common at thermostat connections in the furnace. If there is 24VAC across white and common, then the problem is not likely the stat. Be advised that you may have to trip a door switch so the furnace doesn't think the front panel has been removed.

Thanks! Will try that.

I suspect W1 will be easy to find. Is the common easy to find?

 

[finn]

Logically, if the blower is running, the thermostat is working. All the thermostat does is signal the furnace to begin an operation cycle if the room temp is below the setpoint or terminate that cycle once the setpoint is reached.

If the blower is running, the stat is calling for heat.

 

[The Cobbler]

Logically, if the blower is running, the thermostat is working. ........
If the blower is running, the stat is calling for heat.

OP said the stat is set for the blower to run all the time

 

[zmaxmotorsports]

New stat