When I turn on the heater it works for some time 5-15 until 65-67F then it shuts off. Cool air is blowing. To restart I have to swithch off and switch on the heater (it works if I switch off and switch on t-stat as well). I set 63F last nights, and it worked just fine through the night. In the morning, I set 72 and soon the heater (burning) shut off. Simple LED flashed "system lockout" fault.

Any suggestions?

Thanks.

Furnace is over heating prob' Check filter open all registers and returns, could be a weak or faulty main limit

Thanks.

It was easy: I just replaced the filter, and the heater is working fine, at least it worked in the evening, at night, and in the morning.

Thanks.

It was easy: I just replaced the filter, and the heater is working fine, at least it worked in the evening, at night, and in the morning.
Good to know, If you don't mind, please rate my response.