Pilot is lit, but gas burner doesn't ignite.

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Old 11-04-04, 06:54 AM
sslock
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Question Pilot is lit, but gas burner doesn't ignite.

I have a programmable thermostat, and if it is set to Heat and Auto, the gas burner never turns on, thus the blower never turns on. If I set it to Heat and On the blower turns on without heat. Are there seperate terminals for the gas and the blower? For instance, if it is set to Auto will it tell the furnace to turn on the gas and then the furnace will take care of turning the blower on and off? But if it is set to On, the thermostat will tell the furnace to turn on the gas AND start the blower immediately? Is the W terminal for turning on the gas and the G terminal for turning on the fan?

My guess is that I either have a problem with the W terminal connection between the thermostat and the furnace or I have a problem with the pilot / thermocouple. There is clearly no gas coming out of the burner b/c a) I don't smell it and b) the pilot light would eventually ignite that gas.

Another thread suggested shorting the R and W terminals to see if the burner turns on.

Is it possible that the thermocouple is hot enough to keep gas flowing to the pilot light, but not hot enough to turn on the gas to the burner? Do you think the reason the burner isn't going is b/c the thermocouple isn't hot enough, and if so, is it most likely a problem with the pilot or the thermocouple? I'll check them both out.

Any comments/suggestions?

Thanks.
 
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Old 11-04-04, 09:46 AM
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When you have it on Heat/Auto the burner should come on then the blower will come on low.

Turning it to Heat/On should start the burner and the fan on high.

The "W" terminal is for your heat and low speed on the fan. Shorting R+W should fire up the burner and then shortley after it should start the fan in low speed.

The only time "G" gets energized is if you put the fan switch to on or during cooling mode the stat closes an internal switch with R, Y and G.

You may want to check the programing and make sure the stat is calling for heat.
 
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Old 11-04-04, 09:54 AM
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Wink

You have a lot in the post there .Put it help to know just what you have there for furnace and tstat. You should have heat and cool on the tstat. This will tell what one to come on. That fan on and auto is what it said. When its on auto it should come on after a bit when you ask for heatand the burner is on. When you go to AC the fan should come on right away when the tstat calls for cool. Now when you or on heat or cool and not one is running or calling. You turn the fan to fan on it should run right away.

Like said did you short or jump the R to W??? burner should come on.Does this tstat have batteries in them and are good. Is transformer good 24V???

ED
 
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Old 11-04-04, 11:36 AM
sslock
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I set the thermostat to Heat and Auto. I then cranked it up, expecting the tstat to tell the burner to turn on. The burner never came on, so the blower never started.

I then set the thermostat to Heat and On. The blower turned on immediately, but the burner still didn't come on.

I'll try shorting R to W (can I do this at the furnace, or should I remove the tstat and do it there?) to see if the burner comes on. If it doesn't, what would prevent the burner from starting? If the thermocouple isn't hot enough, could it prevent the burner gas valve from opening. I'm assuming the burner gas valve is seperate than the pilot gas valve.

Thanks.
 
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Old 11-04-04, 12:41 PM
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If R to W lets the furnace light .Then its the tstat If not then its down in the furnace. We know you have transformer power,and if the pilot light stays lit the T/C should be good. When you call for heat check the gas valve see if you have 24V there at that time. If so the gas valve is bad. A meter helps a lot for what you are trying to find out.

ED
 
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Old 11-04-04, 07:43 PM
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It don't matter where you short R - W if the furnace is ok then it should fire up.

Start at the begining. If you short R-to W what happens? "With the fan switch in auto"
 
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