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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I HAVE A LENNOX G26Q3/4-100-3 I have a problem when it is in

Customer Question

i HAVE A LENNOX G26Q3/4-100-3 I have a problem when it is in heat mode of not always kicking on when the thermostat tells it to, but do not have this problem when it is cooling.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: new filter about a month ago and the thermostat check out fine I can even here the click on the thermostat to tell it to kick on and sometimes it does and sometimes it does not if it does not i go to the basement and kill power to it for a couple of minutes and it starts working fine again I have had people come and check this ,but it never does it when they are looking at it.
JA: Do you plan on doing the work yourself?
Customer: depending on what I can narrow the problem to I was almost thinking it could be a solenoid problem
JA: Anything else we should know to help you best?
Customer: no I think that is it
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 8 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

When it doesn't fire up does the furnace respond at all or does nothing happen?

Customer: replied 8 months ago.
it works fine unless it decides not to turn on when the thermostat tells it to
Customer: replied 8 months ago.
i am not at home at the moment so a call would do no good
Expert:  Rick replied 8 months ago.

That doesn't exactly answer my question. It sounds like you're saying when it doesn't work you have a call for heat but the furnace doesn't respond, nothng happens. If that's the case then the most likely culprit is a problem with the thermostat or the thermostat wiring between the stat and the furnace. A partial break in the wiring or a failing thermostat can cause this

Customer: replied 8 months ago.
the thermostat calls for it to turn on and sometimes it does not fire if I reset power to the furnace then it fires and will continue to fire several times when called by the thermostat and randomly one time it will decide not to fire.
Customer: replied 8 months ago.
I had a tech that checked the thermostat and wiring before and said it checked out fine
Expert:  Rick replied 8 months ago.

So the furnace responds to a call for heat but just doesn't fire up intermittently? If so you can you tell me what the LED sequence is on the board is when it doesn't fire?

Customer: replied 8 months ago.
there is no error on the furnace when it does not fire it just does not do anything and I know it was called because I can hear the click at the thermostat
Expert:  Rick replied 8 months ago.

Then you still could have a wiring problem between the stat and the furnace. Did the tech check it out when it wasn't working? If not then his aseertion that's it's all OK is meaningless. That's the nature of intermittent problems and 18 gauge wire is notorious for breaking partially, un-noticed. The other possibilities are much more expensive to fix and harder to trackdown. You could have a bad connection in the control board or possibly a problem with the draft inducer fan (also a bad connection possible). If the inducer doesn't run then nothing else will happen.

Customer: replied 8 months ago.
The draft inducer fan would that possibly start and shutdown quickly because sometimes when I reset power a fan will kick in and shut down almost immediately then a few moments later kick back on and everything is fine.
Customer: replied 8 months ago.
Also why would this not be a problem when it is cooling if it were to be a thermostat wire
Expert:  Rick replied 8 months ago.

Cooling is an entirely different circuit and runs off different leads in the thermostat cable. The fan behavior you descibe doesn't eliminate any of the possibilities.

Expert:  Rick replied 8 months ago.

Do you have any more questions?

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