Gas and Oil Home Heating Furnaces - furnace problems
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MJR
10-20-06, 02:51 AM
I have a Lennox gas furnace model G12D-82-4, manufacture date of 1/86. 82,000 btu's, in a 50 year old house about 1,000 sq ft and I have a issue I am hoping someone can help with.
This started last year with the burners cycling on and off about every 30 to 45 seconds, and blow out the pilot light every once in a while. The fan/limit switch would click about 4 times, then shut the burners off. I could hit the switch and the burners would come back on for a bit. I have replaced the fan/limit switch last year, was still having the problem. I had a repairman come and look. He was suggesting the furnace was tripping the high limit and found no problems, no blockage and the heat exchanger looked ok, so he turned down the gas pressure a little and it seemed fine the rest of the heat season.
When i turned it on a few days ago, it was doing the same thing, cycling, fan/limit switch clicking etc...I left it off for a few days and tried to turn it on again, only now i have no burners, but the pilot is still lit. The t-stat clicks on for heat, it has the delay of the burners, then the blower starts, but no burners. The blower will run until i flip the switch on the t-stat.
Is it possible the fan/limit swtich is bad again? It has a "cam stat" and the limit is set at 200 degrees and the fan off is set at 100 degrees, it has the pre heater wires going to it too.
Thanks
This started last year with the burners cycling on and off about every 30 to 45 seconds, and blow out the pilot light every once in a while. The fan/limit switch would click about 4 times, then shut the burners off. I could hit the switch and the burners would come back on for a bit. I have replaced the fan/limit switch last year, was still having the problem. I had a repairman come and look. He was suggesting the furnace was tripping the high limit and found no problems, no blockage and the heat exchanger looked ok, so he turned down the gas pressure a little and it seemed fine the rest of the heat season.
When i turned it on a few days ago, it was doing the same thing, cycling, fan/limit switch clicking etc...I left it off for a few days and tried to turn it on again, only now i have no burners, but the pilot is still lit. The t-stat clicks on for heat, it has the delay of the burners, then the blower starts, but no burners. The blower will run until i flip the switch on the t-stat.
Is it possible the fan/limit swtich is bad again? It has a "cam stat" and the limit is set at 200 degrees and the fan off is set at 100 degrees, it has the pre heater wires going to it too.
Thanks
Grady
10-20-06, 04:16 PM
If you turn the thermostat up all the way & it works, I would suspect a problem with the thermostat. If you get the same symptoms, the fan/limit could be bad or maybe another limit. Many furnaces have more than one.
MJR
10-21-06, 01:44 AM
Thanks, I will try that. I'm hoping it's not the fan/limit switch, as i have gone through 3 of them since last year at $55 a pop, but i guess it's still cheaper than a new furnace, which i may look into replacing next year.
MJR
10-22-06, 06:19 PM
I tried turning up the t-stat all the way up, and the burners lit for about 10 seconds, then went out, and i think i have only have one fan/limit switch. There is a small oblong shaped ceramic switch of some kind that has 2 wires going from it to the gas valve, and on the gas valve, it's marked ECO. Could that be another limit switch?
Grady
10-22-06, 07:15 PM
The ECO is an Electic Cut Off switch. This switch must be closed to keep the gas valve open. The oval ceramic device is probably a fuseabe link. About all I can tell you at this point is to trace voltage & see where you loose it. Maybe one of the other guys have some ideas.