Furnace turns off before reaching preset temperature

Old 12-03-11, 07:26 PM
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Furnace turns off before reaching preset temperature

I have a Lennox ghr32v furnace that will not turn back on after the temperature drops below the preset temperature settings. It will start up again if I turn the heat on the thermostat off and then turn it back to heat again. It will then turn off before it reaches the desired temperature and not turn back on again until turning off and on heat (resetting the thermostat?). I replaced the thermostat but the problem persists. I have replaced the filter (high end, small particle filter). I have drained the water and checked the draining which appears to be working.

Ideas Anyone?
Old 12-03-11, 08:03 PM
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check the diagnostic LED lights through the blower door viewing window and compare with the legend on the door.
Old 12-05-11, 12:45 PM
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When my old furnace behaves like that:
1) The blower wheel is fouled. It takes just a little crude on the blades to reduce the efficiency to the point it does not move enough air to operate the furnace and it shuts itself down. I suggest actually removing any blower wheels and visually inspecting them. Anything more than a layer of dust needs to be cleaned.

2) The exhaust flue or chimney is partially blocked. For example the clay liner is disintegrating or an animal built a nest. The clay liner can be replaced and capped with something that will discourage animals btw.
Old 12-05-11, 01:13 PM
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Something is probably shutting off the furnace. You need to determine what that something is. Guessing is not sufficient.

Checking the diagnostic codes is a good place to start.

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