Lennox furnace fan runs continuously


Old 10-16-08, 08:39 AM
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Lennox furnace fan runs continuously

I have a Lennox G8-110 gas f/a furnace (house was built in the 70's, and it is probably original equipment). The thermostat works fine, and the gas turns on & off, heating the house fine. But the fan runs continuously. This of course is hard on the motor & fan, and cools the house faster, so we burn more gas.

I know there should be a thermostat in the Plennum, but cannot find it. Any ideas? Am I on the right track?

Many thanks.
David Y
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Old 10-16-08, 04:14 PM
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I can't think what an f/a furnace is.

If your thermostat mistakenly did not wind up getting set to a fan ON setting, then the problem likely is that a fan switch in the furnace is stuck on. I am not sure what kind you have. Some older furnaces relied on a thermodisc type switch that is superficially mounted on the sheetmetal inside, above the burners. Some had what looked like wires that just connected onto spades on the sheetmetal of the furnace above the burner area inside(with the heat sensing device inside where you can't see it at all). There are various sorts.

But what you can do to DIY locate it, is to trace wires from the blower, inside the blower compartment, and it will travel into the other compartment that has the burners, and at least one of these wires is going to wind up connected up to some sort of thing that has at least one OTHER wire on it, and this thing will be mounted on the sheetmetal above the burners. This thing will have a minimum of 2 wires on it. One hot 120 volt wire feeding it, and the other 120 volt wire that is activated by heat, and then when activated, sends the current down to the blower. If this thing is stuck closed so the contacts in it are bridged, obviously the fan would just keep running.
Old 10-16-08, 05:52 PM
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As old it may be, you may have a fan/limit control.

It may look like something like this above, and if that is what you have remove the cover, and will have a dial. See what the ON set point it at.

Some will have this one below.

If you have a meter, take a reading across this and see if may be your issues.
Old 10-20-08, 07:57 PM
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I can't think what an f/a furnace is.

F/A........................... forced air furnace
Old 10-20-08, 08:01 PM
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[QUOTE=ecman51`;1447429]I can't think what an f/a furnace is.

f/a furnace.......................forced air

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