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type2technician, HVAC Technician
Category: HVAC
Satisfied Customers: 241
Experience:  Heating and a/c repairs
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I have a Lennox ML180UH nat gas furnace that will not

Customer Question

I have a Lennox ML180UH nat gas furnace that will not ignite. The glow pilot does glow and the gas valve will not open. The circuit board code lights red and green flash at the same speed and time and just keeps recycling. It does not leave any other error codes. Where can the problem be.
JA: Did you double-check the thermostat? And what about the pilot light?
Customer: Thermo stat appears to be functional. The glow runs for a few seconds but no pilot. Do not get power to gas valve.
JA: Do you plan on doing the work yourself?
Customer: Yes I am a lic plumber for 45 years.
JA: Anything else we should know to help you best?
Customer: Not that i can think of
Submitted: 9 days ago.
Category: HVAC
Expert:  type2technician replied 9 days ago.

This sounds like the pressure switch is not closing which the igniter will not glow red until the pressure switch closes. Remove the top furnace cabinet door. You will see a inducer fan motor that connects to the flue exhaust vent pipes. Locate the inducer fan motor, then remove the rubber hose that connects to the inducer fan motor and the pressure switch. Use a paper clip to clean out the connection on the inducer fan motor very good applying force if necessary. The paper clip should go all the way through touching the fan blades. Also inspect the rubber hose for any breaks or tears. If there are any breaks or tears, replace the hose. After you have cleaned the inducer fan motor connection, place the hose back.

Customer: replied 9 days ago.
Pressure switch appears fine. Glow plug does light and glow. No pilot..!!
Expert:  type2technician replied 9 days ago.

I apologize. Has the gas been cut off at the house? Can you verify?

Customer: replied 9 days ago.
Gas Stove and fireplace work fine.
Expert:  type2technician replied 9 days ago.

Do you have a voltmeter?

Customer: replied 9 days ago.
Expert:  type2technician replied 9 days ago.

Shut the power to the furnace off then back on again. After the igniter glows red, use your voltmeter to check to see if the gas valve is receiving 24 volts. There should be two wires attached to the gas valve. Remove them and use the voltmeter probes to check for 24 volts.

Customer: replied 9 days ago.
No power to gas valve
Expert:  type2technician replied 9 days ago.

This means that the control board on this furnace has gone bad. It will have to be replaced.

Customer: replied 9 days ago.
I will go pick one up. Can I get back to you once I replace it and still have a problem if necessary.
Expert:  type2technician replied 9 days ago.

Yes. After you have rated this session, you can access me for up to 30 days.

Customer: replied 9 days ago.
Thank You
Expert:  type2technician replied 9 days ago.

thanks for using Just Answer! Please rate this session so the expert can be paid. Thanks

Expert:  type2technician replied 6 days ago.

Hello. I hope that you were able to repair your heating system. If you were satisfied with our session, Please rate the session so the expert can be paid. Thanks for using Just Answer!