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Hello, I am looking for some help regarding my 2 yr old Lennox ML180UH furnace. When it begins the start-up sequence, the inducer motor kicks on, then the ignitor glows and then after about 25-30 seconds it either opens the gas valve and the burners light or it clicks/clunks, shuts down the inducer motor and after about 2 seconds begins the start-up sequence again. The furnace probably ignites on the first start-up cycle about 85% of the time. However, it can take 2-4 start-up cycles to ignite the remainder of the time. In all cases, the furnace ignites and heats as directed by the thermostat.

We have had our HAVC technician out to fix the problem. First, he replaced the control board since he was getting “screwy” voltage readings of ~14v when it should have been 0. This didn’t resolve the issue and after speaking to his supervisor was told that Lennox often has this intermediate voltage reading, but it is “normal.” He and the supervisor then determined that it must be the gas valve that is the issue and it was replaced about 6 days ago. This still hasn’t fixed the issue as last night it averaged 2-4 start-up cycles per ignition.

Before having the HVAC technician out again, I was hoping that those on this forum could provide some guidance.

As I understand the start-up, the inducer motor turns on, once appropriate draft has been developed as measured by the pressure switch, the ignitor glows and then after a certain amount of time, the gas valve opens and the burners ignite.

Any ideas on what could be causing the start-up sequence to not complete and opening the gas valve?

Is there another sensor that must be met to allow the gas valve to open?

Any help/suggestions would be appreciated as I wanted to be more informed before I call the HVAC Service Company and speak to the owner.

Thanks!
 
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