I have York diamond 80 furnace. It is about 12 years old and works fine. Except one problem happens intermittently. Once a day or a few days, the furnace blows hot air.
Once it reachs the set temperature, it will not stop and keep blowing hot air and then
Change into room temperature air. Turning off in the thermostate will not shut it. I have to turn the furnace off from the circuit breaker and then everything start working again
For sometime. This is seems happens more often in the morning when the day temperature kick in and the furnace is working very hard to bring up the house temperature.
I have search the internet and cannot find anyone with similar problem. Would you please let me know what is my problme and how should I debug it? By the wayl, the filter is seems clean.

I have the same problem as well. Did you have luck figuring it out?

Well if you are saying that the blower stays on then your blower relay is not working. It is located on the control board. If it does not have a board then you can get just the relay. Otherwise you need a bosrd. I hope this helps you.