Controls *: heating cutting out

[phand]

Hoping someone can give me an idea where my problem is. I have a York Diamond 80 which is probably more than 15 years old. It heats fine, and the air conditioning unit works fine as well. Last year there seemed to be some problem with the thermostat so we got a new one, an inexpensive Honeywell. The problem went away but not completely. This problem is only with the heating unit, not a/c.

What happens is that we can turn on the heating unit, but at certain times it just changes by itself and stops blowing hot air. Instead it just blows cool/ambient air, and it won't stop, even turning off the thermostat. So I have to go down to the basement, turn off the main switch, and then turn it back on again, and the unit works fine, heating until it reaches the temperature setting.

I haven't figured out the frequency this happens, or what my set it off. If it happens in the middle of the night, we have to turn it off once, and back on, and it doesn't happen again.

Anyone have an idea about this and how to cure *

[heatseeker]

sounds like a stuck high temperature switch or perhaps a stuck relay kind of hard to tell from here but next time it happens don't touch it and call a service comp. so they can diagnose it properly.

[surenuff]

The above answers are things to check, but also check the flame sensing rod. Sometimes they will intermitently not prove that the flame is present which will cause the unit to cycle through the ignition sequence again. If it does this a couple time and does not prove the flame, it will lock out the board and leave the motor running until power is killed to the board which resests it.