I have a honeywell th8000 thermostat and a rheem gas heater /ac system.
I have a intermittent problem where the temp goes below the stat setting and heater does not come on. I have to turn the heater off from the stat and back on again and it will run fine. This happens once in a while night or day, mostly night. Could this be the stat or the heater?

[email protected]

Could be either, but don't rush to blame the thermostat. If the furnace malfunctions and activates a timed lockout, the action of switching the thermostat off/on will cancel the lockout. Look for diagnostic LEDs on the furnace that may provide clues.