I have a Lennox system that is four years old. Recently, after a pwr outage, both of my thermostats have had the pwr light go out and the system does not work, except for the blower continuously running. The weird part is if I leave it alone after a few hours the system starts working again, and the pwr lights are on. This has been going on for a week and the system will run for a day and stop and than start again. The AC guy came out one day and he could not find any thing wrong with the system, freon was OK and all the electrical voltages were normal. He suspects a circuit board in the furnace but is not sure without replaceing the $167 part, which I buy weather it fixes the problem or not. Any ideals?


Thanks for any help :confused:

Power outages are extremely hard on electrical equipment. I think the modern automatic switching equipment makes it even worse as it cuts off and back on several times before it goes off and stays off and another cycle when it comes back on. The outage could have messed up either the thermostats, or the furnace controls, or even the blower and compressor.

If both thermostats go out at once, I would suspect the transformer that feeds them. It may be separate from the circuit board, and much cheaper. Most HVAC systems use a 24 volt one you could pick up at a home center or even Radio shack for less than $10. Just make sure the amps output is as high or higher than the old.

I think a lighting storm killed the board in my furnace, $300+. The new one has varistors protecting it.

I also turn off or unplug stuff while the power is off, leaving a few lights to let me know. That way my refrigerator skips fighting everything else for voltage when the power comes back on.