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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22680
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Lennox furnace won't start. What could be the reason?

Customer Question

Furnace won't start. I have a Lennox G61MPV Furnace with a Lennox Elite Series 3 Programmable Thermostat. We have noticed once in a while some "disconnect" in the past between what we have programmed and what the furnace actually does, but starting yesterday the furnace doesn't come on at all now. We have 75 people coming for an open house this evening and it's 35 degrees outside (60 inside.) Any ideas?

Submitted: 7 years ago.
Category: HVAC
Expert:  BillyHvac replied 7 years ago.


Sounds like a big day!...Can you tell me if a red light is visible through a small viewing port in the bottom door of the furnace?

Customer: replied 7 years ago.
I will go look and be back. . .
Expert:  BillyHvac replied 7 years ago.

See page 91 here -

This is the specific service manual for your unit. Page 91 starts the description of fault codes.

Customer: replied 7 years ago.
OK, I see just one light and it's flashing green. . .
Expert:  BillyHvac replied 7 years ago.

A constant pulse is normal as shown on page 33 here -

Do you mind removing the thermostat top section for a test?

Customer: replied 7 years ago.
OK, what do I do?
Expert:  BillyHvac replied 7 years ago.

Remove the top section to where we can see the thermostat wires and where they attach.

We want the wire on terminal R (could be RC,RH) that is commonly red, and the white wire on W (could be W1)....we want to twist those 2 together or touch them at same time with short wire or paper clip shaped in a U.

The goal is to connect the red wire to the white wire. This bypasses the thermostat and will tell us if we have a thermostat issue or furnace issue.

When red and white touched together the furnace should start.

Customer: replied 7 years ago.
OK, they are touching (connected with a paperclip), but no response from furnace
Expert:  BillyHvac replied 7 years ago.

Thank you.

Now reassemble thermostat, turn power off to furnace for 10 seconds, turn back on, thermostat back up.

Then tell me exactly what the sequence is including the flash code.

Customer: replied 7 years ago.

?? Not sure how to turn power off to furnace. I can turn thermostat to "off" (from "heat" or "auto"). Is that what you mean? Or do you mean flip off the breaker to the furnace? And does the "flash code" show up on the thermostat screen or the two little lights (one that's off, the other flashing green) I can view through furnace door?

Expert:  BillyHvac replied 7 years ago.


Cut power to furnace via breaker or power switch on side of furnace.

The lights with fault codes will be visible through the small port in bottom door of furnace.

Tell me if any noise or operation happens with furnace also.

Customer: replied 7 years ago.
Both LED lights are flashing green. There was a brief "click" when I turned power back on, but nothing else. . .
Expert:  BillyHvac replied 7 years ago.

Flashing at same pulse or alternating?

Customer: replied 7 years ago.
Same, rapidly. . .
Expert:  BillyHvac replied 7 years ago.

There is a small exhaust fan in the upper section that usually starts first. Does the motor feel cool or hot?

Customer: replied 7 years ago.
The LED lights have gone back to their earlier state: the left one is off, the right one is flashing green slowly. As for the fan, I'm not sure I can see that, but nothing on the furnace itself is warm or seems to be operating at all - total silence
Expert:  BillyHvac replied 7 years ago.

Ok we are going to try something....

In the top section is a pressure switch. It has rubber tubing going to it that air is pulled through to activate a switch. It also has a couple of wires to it.

See page 23 if you need location.

Tap on those switches, remove the rubber tubes and make sure the tubes and ends are clear. I am hoping one of these switches just got stuck closed. Reassemble and try furnace.

Customer: replied 7 years ago.
OK, I tapped on the switches, and pulled on the rubber tubes connecting the switches but didn't remove the tubes for fear of breaking the plastic switches. While doing that, however, I did discover that the fan motor is warm. You asked me about that earlier. . .
Expert:  BillyHvac replied 7 years ago.

Thank you.

The concern I had is with the red and white wire jumped. The very first thing to happen is the circuit board evaluates various inputs, and then starts the exhaust motor. Possibly the click you hear is the relay telling it to run.

The motor may not start because it is bad, stuck at a "dead spot" in the motor or a object/rodent/bird has made its way to housing and has the motor stuck.

The goal now is turn off power and find a way to see if the motor assembly can turn freely.

Customer: replied 7 years ago.
OK, I turned off power. Sorry, not sure what you mean by "motor assembly." If you mean the big encased circular fan, yes, it turns freely when I reach in and rotate it. . .
Expert:  BillyHvac replied 7 years ago.

Page 23 - combustion air inducer.

It is the motor assembly that the plastic pipe attaches to.

Customer: replied 7 years ago.
OK, I can't figure out a way to see if that part moves. It's the combustion air inducer that is warm. . .
Expert:  BillyHvac replied 7 years ago.

Ok, that is our stumbling block. The motor is either bad or stuck. Unfortunately I am in a hands off situation where I can only go so far. The rest would require using a meter to ensure 120v to motor and that it is not stuck.....

I apologize, but that is where we are at.

Customer: replied 7 years ago.
Assuming a motor problem, any guess on repair cost (and time to repair?)
Expert:  BillyHvac replied 7 years ago.

Lennox dealer will be able to tell depending on motor in stock. So call a Lennox dealer for service.

Bad news...could be $400-$500 bucks total. If it is a bad motor. It comes as the entire motor, housing, wheel etc.

BillyHvac and other HVAC Specialists are ready to help you
Customer: replied 7 years ago.

OK, thank you. . .