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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 7980
Experience:  Furnace, A/C and heat pump specialist.
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Lennox G26 series furnace will turn on, but won't light.

Customer Question

Lennox G26 series furnace will turn on, but won't light. Diagnostic codes are diag no. 1 is off and no. 2 is flashing.
Submitted: 3 months ago.
Category: HVAC
Expert:  airheatman replied 3 months ago.

Does the small inducer vent fan come on when you call for heat?

Customer: replied 3 months ago.
Vent fan does come on
Expert:  airheatman replied 3 months ago.

OK, This indicates that the pressure switch is not closing.

Below is a flow chart listing causes and corrective steps.

Lets start by removing the hose and blowing through it to make sure it is clean.Use a straightened paper clip to clean little barbed fittings.We will go from there.

Customer: replied 3 months ago.
There are two small hoses coming from the pressure switch. I removed both, and both seem to be clear and air is able to flow through both.
Expert:  airheatman replied 3 months ago.

Any water in the hoses at all? Go ahead and with hoses attached to switch suck and blow on them and see if you hear pressure switch click

Customer: replied 3 months ago.
No click
Customer: replied 3 months ago.
No water
Customer: replied 3 months ago.
Sorry, it did click. Very faintly
Expert:  airheatman replied 3 months ago.

If switch does not click you most likely just have a bad switch.Contacts not closing.Do you have a volt meter to see if the switch is closing?

Customer: replied 3 months ago.
It clicks twice actually
Expert:  airheatman replied 3 months ago.

Ok if switch clicks that is good.Now reconnect hoses and try furnace listening to see if you hear the clicks when inducer starts rather than by sucking.

Customer: replied 3 months ago.
It clicks and the fan comes on, the fan stops momentarily, then it clicks again and the fan again comes on
Expert:  airheatman replied 3 months ago.

Fan should not be going on and off,It should stay on entire heat cycle. Do you have a meter to see if we are losing voltage to inducer?

Customer: replied 3 months ago.
I don't have a meter.
Expert:  airheatman replied 3 months ago.

OK your problem is the pressure switch is not staying closed.You will have to get a tech in with a meter to troubleshoot to determine why motor is cutting off and pressure switch not closing.

Customer: replied 3 months ago.
I'm trying to get a meter from my neighbor. I'll get right back to you.
Expert:  airheatman replied 3 months ago.

Great. What we wan to do is check leads to meter for 120 volts and see if the voltage is dropping out when fan stops.

Customer: replied 3 months ago.
Meter reads 23
Expert:  airheatman replied 3 months ago.

OK if we are only getting 23v to motor this is an issue with the control board,It should be sending 120v the entire time furnace is calling for heat.

Customer: replied 3 months ago.
that doesn't sound like an easy fix?
Expert:  airheatman replied 3 months ago.

Most likely will have to replace board.If it is something you want to do you can do yourself, but I would feel more comfortable having an onsite tech verify.

Customer: replied 3 months ago.
Ok, I'll call a tech.
Expert:  airheatman replied 3 months ago.

Wish it were a simple fix like condensation or debris in the hose, but since motor is quitting seems to be more involved.

If you have further questions, please let me know.

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Customer: replied 2 months ago.
I just re read this thread. I'm getting 23 volts to the switch. I'm getting 120 to the motor.
Expert:  airheatman replied 2 months ago.

OK is the 120 staying constant when motor quits? You stated "It clicks and the fan comes on, the fan stops momentarily, then it clicks again and the fan again comes on "