forced air furnace won't ignite...

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Old 04-19-04, 01:04 AM
calamitytam
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forced air furnace won't ignite...

I have an older forced air furnace that won't ingnite when the thermostat is turned up. The pilot light is on and there is a buzzing noise that I believe means that it is calling for gas, but the main burner won't ignite. I installed a digital thermostat earlier last year and this problem started when it got hot enough during the day for me to turn the furnace off rather than setting the temp lower. When I went to turn it back on, it won't light.
 
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Old 04-19-04, 07:48 AM
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Could be the gas valve . But take and jump R to W there at the tstat The burner should light If it does it could be in the tstat. Just how old is old for the furnace? Does it have a control board in it?

ED
 
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Old 04-19-04, 09:18 AM
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Does it have a pilot light or an auto ignitor? If it's a pilot light system, the thermocouple may be shot. A new one should cost around $10.
 
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Old 04-19-04, 11:34 AM
calamitytam
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FORCED AIR FURNACE PROBLEM

THANK YOU FOR THE ADVICE. I JUST TURNED THE PROGRAMMED THERMOSTAT TEMP DOWN UNDER WHAT THE ROOM TEMP READING WAS, TURNED THE FURNACE OFF FOR ABOUT AN HOUR, TURNED IT BACK ON, TURNED THE PROGRAMMED TEMP UP ABOVE WHAT THE ROOM TEMP READING WAS AND THE FURNACE CAME ON. I HAD TRIED THIS BEFORE AND IT DIDN'T WORK. I HAVE DONE SOME RESEARCH ON LINE ABOUT ME TYPE OF FURNACE AND IT IS LIKE THIS: IT IS FROM ABOUT THE LATE 1970'S WITH A PILOT LIGHT THAT STAYS ON ALL THE TIME. UNFORTUNATELY THE WAY THE GAS LINE IS RUN ON THE FURNACE, I WOULD HAVE TO DISCONNECT MOST OF THE GAS LINES TO THE FURNACE, AND REMOVE THE MAIN BURNER TO HAVE ACCESS TO THE THERMOCOUPLE. I HOPE I DON'T HAVE THIS PROBLEM AGAIN.
 
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Old 04-19-04, 11:49 AM
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UNFORTUNATELY THE WAY THE GAS LINE IS RUN ON THE FURNACE, I WOULD HAVE TO DISCONNECT MOST OF THE GAS LINES TO THE FURNACE, AND REMOVE THE MAIN BURNER TO HAVE ACCESS TO THE THERMOCOUPLE.
The T/C should just pull out or unscrew from the pilot light there. Then just unscrew out of the gas valve is all


ED
 
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Old 04-19-04, 11:54 AM
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often the pilot assembly will come out with one screw. use a long handled nut driver. if it has a magnet it will make putting it back together easier
 
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Old 04-20-04, 05:10 AM
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Hello: calamitytam

Older furnace is very generic. Some older furnaces are horizontal designs. The burners in those types do require the gas inlet line to be removed from the control valve so the burner tray can be slide out to access the pilot assembly.

The pilot assembly in some horizontal furnaces have the pilot assemblies in the center of the burner assembly. Thus the need to slide out the burner rack (tray) to access the pilot assembly.

Most likely, based upon your description of having to remove the gas supply inlet line from the gas control valve first, I can reasonably and hopefully assume the furnace is a horizontal design versus a vertical upright furnace. >Is this correct?<

Disconnect electrical power and turn off T-Stat prior to attempting any repairs!!!

Once the burner rack (tray) is slide out about halfway, the pilot assembly is readily accessable. Remove the thermocouple from the pilot assembly, blow out the entire pilot assembly to remove any accumulated dust.

Use canned compressed air to cleanout pilot assembly. Canned compressed air used to clean computer keyboards, etc work well. Blow out entire pilot assembly including all holes found.

Than install new T-Couple exactly as the current one is installed. Than slide tray (Rack) back in, resecure it with screws as found prior. Reconnect wires and gas inlet line as found & exactly as found prior to disassembly.

Relight pilot as usual. Reconnect or turn on electrical power. Turn on T-Stat and all should be well. Soap test gas connection to insure not gas leak exists. Job should than be completed....

Side Note:
There are some vertical (updraft) furnaces with center located pilot assemblies. Same basic procedures required to access pilot assemblies. (Vertical updraft means blower beneath furnace.)
 
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