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QUESTION:My furnace stops before the set temperature is reached. I am in NJ where
it is rather cold these days. I have been observing the furnace closely
and this is what I saw.
NOTE: This only happens in the morning, I set the thermostat really down
at night (55F). Day setting is 66F.
When thermostat kicks off the heat, my Lennox high efficiency (model
G26) turns on the air intake pump (brings air in from outside of the
house). After about 10 seconds, burners come on. Then 10-15 seconds
after that - main fan comes on. After about 5 minutes, fan and the
burners shut off but the fresh air intake fan keeps running and this fan
runs forever unless I shut off things from the thermostart and restart.
After I do this 3-4 times, things run fine all day.
When the system was working fine, burner and the air intake fan would
stop first (after proper temp was attained) and 20 seconds later, main
fan also would turn off.
Thermostat doesn't seem to be the culprit because I stood there to see
if there is any click indicating a signal from it to the unit.
So, it seems that the problem happens only when the home temp is very low.
ANSWER: The only way the filter would be a problem is if the furnace is shutting off
on high temp limit --not enough air getting thru the heat exchanger. Then
the furnace surely would not run correctly when the circulating air is
warmer.
It sounds like it might be some kind of problem in the control circuitry
(call a mechanic), but I noticed a posting here earlier where the pvc
intake/vent pipes were freezing up. I am sure this will cause strange
behavior at the furnace when it happens, so it might be worth inspecting the
vent plumbing the next time this happens. I would expect freeze-up only to
be a possibility at very low temperatures, colder than NJ, but who knows?
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