My heater will turn on and run 1 cycle. But to get it to turn back on, I have to go and either turn it up a degree, or sometime turn switch to off and then back to heat. It will then run 1 cycle again. Replaced thermostat from old round 1 to honeywell digital. Any ideas?

May need to clean the flame senser.

Sorry forgot to add we have replaced the ignitor, the flame sensor and the thermostat

What kind of heater is it. And how old? If it is a 90+ unit )plastic vent), the drain system in the furnace may be clogged. If so, clean all hoses, and ports where hoses hook too, and any trap that is in the furnace.

It's a Goodman that was installed about 5 years ago. I'll give that a try thank you!