Lennox Furnace won't stay lit


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Old 01-17-09, 08:37 PM
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Lennox Furnace won't stay lit

We have an older model Lennox furnace. A G 11. Two years a go, we had it looked at by a friend who was retiring from his heating business. He said we could probably get a few more years out of it, then wed have to replace it. Last spring, right before it got warm, the gas would go off, and it wouldn't shut the gas off automatically, and we could smell it in the house. Our friend told my husband to replace the gas valve, which he did, with a Honeywell. He told us to replace the thermocouple too. Then we had a problem with the thermostat, so he replaced that too. The problem is now that the furnace will light, and it goes on for around five minutes, then it goes off. I have ice on my windows! Can anyone else think of something we might try, or are doing wrong? We are on an incredibly tight budget this winter and cant afford to replace the furnace now. Thanks!
 
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Old 01-17-09, 09:12 PM
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The most likely problem us that the burners are shutting off because the furnace is overheating.

The most common causes of that are a plugged furnace filter, a covered over cold air return or warm air vents that have been closed off. Also, a plugged AC evaporator coil in the furnace can cause that problem.

So I'd check those.

Do it yourself repairs have their limitations, and one is that even if you fix acute problems, you often don't do the inspections and maintenance needed to keep a furnace operating safely, especially an older furnace.

Perhaps you can get your retired friend to come over and do that for you ---we retired furnace repairman often don't mind doing such tasks as long as they don't amount to holding down a job.

But if he can't do that work, perhaps he can recommend an honest and competent repairman in the field to help you maintain the furnace. That would be a VERY valuable reference in any case.
 
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Old 01-20-09, 12:47 PM
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If the short cycling problem started after the thermostat was installed then it may be as simple as having to properly set the anticipator on the thermostat. But if your new thermostat is digital then that won't be the case. You may be better off hiring someone to at least diagnose the problem for you. Can you hear the blower operating? May have a bad fan/limit control or blower problem. Furnace could be cycling on and off from tripping high limit and then cooling down enough to re-light burner.
 
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Old 01-20-09, 01:05 PM
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Another possibility is that the new gas valve wasn't set properly to match the furnace. Replacing the gas valve is not a repair I'd generally recommend for a do it yourself project.
 
 

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