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Gas Furnace Trouble Shooting
QUESTION:I have a thirty-year-old Lennox G10R series forced air natural gas
furnace that has suddenly gone haywire. Sometime around 6AM this
morning, the furnace came on and just kept running. I awoke to an 80
degree room realizing that something was wrong. I have a newer
programable thermostat that was set for 60 degrees at the time so the
unit shouldn't have even come on as it has been mild here in the
Pacific Northwest. So one thing is that I am confused as to how the
unit called for heat in the first place. But even so, why wouldn't it
shut off? I had to turn the power off to the furnace in the garage to
stop it from running. Everything else seems to be working fine
(blower, etc.) Sounds like a thermostat problem to me but how does
one tell? Also, I reprogrammed the thermostat and tried to turn the
power back on and the heater still wants to run even though the
thermostat is set 10 degrees below the room temperature. Another
trick that I tried was to remove the thermostat from its mount (it's
"armchair" programmable) and the furnace still fires-up and heats
making me think that maybe it's something else. Any assistance with
troubleshooting this would be immensely appreciated. Just knowing
what the suite of possibilities is would be a great help.
ANSWER: since you say you removed the thermostat from the base and it
continues to run you have most likely got a stuck relay inside the
furnace that requires a pro's attn.
considering the age of the unit, other problems may soon follow so
weight the expense of a service call to make this go away agianst
replacing the system. the system should have lasted 17 years so you
got some extra out of it compared to the average. it has no value and
the units today will cost you one heck of a lot less to operate and
will result possibly in enough reduction in your electric bill over a
couple of years to pay for themselves.
if you absolutly must poke around inside your unit use caution and
know it can and will kill you if your fingers touch the wrong part
with electricity applied to it. look at the diagram and see what makes
heat work and check those things and see if you can figger it out. you
also need to be careful in what you decide to test and check because
you can also make a simple repair more costly by making a mistake.
you should call a pro and get back to feeling cool or comparing bids
on a new system.
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