Lennox Furnace problems


Old 12-18-08, 11:30 AM
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Join Date: Dec 2008
Posts: 2
Lennox Furnace problems

I have a furnace from '97 with a honeywell thermostat bought in 05

no problems until last weekend, when it failed to start heating even when the thermostat has the "heating" display showing. The furnace does start after switching the master switch off/on, then it would heat the home normally for the rest of the day until the morning, im guessing its not starting after a long time of inactivity because I set the period between 12am - 9am to 16C instead of the regular 18C during day time.

I took out the flame sensor yesterday to scrub it clean with sand paper by advice from the net/inspector who couldnt find anything wrong with the furnace since it was working when he came. But it was cold again when i woke up this morning, down to 14C when the thermostat is set to 18C.

anyone know what the problem might be? thanks
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Old 12-18-08, 04:01 PM
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Join Date: May 2007
Location: Wisconsin
Posts: 8,629
It must have locked out after several attempts to run, and fail.

You are going to have to intentionally replicate when it does it and go down there and open up the main biggest panel to furnace and see what happens in the sequence. See if the inducer motor even bothers to come on. Or if it comes on and quits (if so, when?). Or if a pilot light comes on and quits (if so, when?). Or if any type of iignition fails to ignite. Or if the igniton does occur and there is burner fire, but then it quits (and if so, how long does it run before it quits?).

What IS the type of ignition you have?: Direct spark to burner(s)? Or one of those glow coils? Or spark to a pilot?
Old 12-19-08, 07:44 AM
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Join Date: Dec 2008
Posts: 2
i do not know the type of ignition, i hear short quick bursts that sounds like electricity snaps before it come on, like 10-15 snaps in real quick successions

its hard to replicate when it fails because it does it at night only it seems, when i power it off/on in the mornings it stays fine for the rest of the day

btw its a Lennox G20 whisperheat furnace, with what i assume to be stock parts since we didnt change anything since buying the house in 2004

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