Hi,
I have a Honeywell "CT43-A-4440" 750 millivolt thermostat controlling our gas fireplace - but of course I've lost the owner's manual :o (I can't find the manual on the Honeywell site either)

My problem - the thermostat calls for heat correctly but once the room has reached the target temperature it cycles the fireplace off and on rapidly 10-15 times. By "cycling" I mean it calls for flame, then a second later it shuts it down again.

There's a small screw inside the thermostat that I suspect is an adjustment but I'm not sure which way to turn it, how far to turn it, etc. (or even if the screw is what I need to adjust).

Any help would be most appreciated.

Thanks

I would say if it has been working fine for a while, you don't need to adust it, replace it with a new millivolt thermostat gold contacts are better

There is a sticky in the Electrical forum with links to thermostat manuals.