I have 2 gas fireplaces in 2 separate cabins - one will not ignite when the thermostat calls for heat and one ignites when I turn the knob from pilot to on and will not shut down when the thermostat in turned down - last yr I had the same problem with one - I cleaned the thermostat wires with sandpaper and it worked - not this time - labaman can you help? Regards.

There should be two wires at the thermostat, remove one, if the fireplace shuts off, replace the thermostat. Does the fireplace that won't light have a pilot light? What brand fireplaces are they? Do they have power ran to them or are the gas valves powered by a thermopile?

There should be two wires at the thermostat, remove one, if the fireplace shuts off, replace the thermostat. Does the fireplace that wont light have a pilot light? What brand fireplaces are they? Do they have power ran to them or are the gas valves powered by a thermopile?

They both have pilot lights with thermocouplers and are made by regency.

Do they have wall mounted thermostats? I'm guessing they have milivolt generators, the one that won't fire may have a bad generator (thermopile),try bypassing the thermostat,if it still will not fire,replace the thermopile,it's located right next to the thermocouple on the pilot assembly. The one that won't shut off,try disconnecting the thermostat.

Yes they have wall mounted thermostats - and say 750 millivolt on them - do I have to use the mercury ones or can I go to a higher quality thermostat - something seems to always go wrong this time of yr when I fire them up for the winter -

Any kind of low voltage thermostat should work.

Here is a bit of gas fireplace info for you to keep.
This is the Regency web site manuals. While your exact manual might not be available almost all gas fireplaces operate the same way within a brand name. Down load or keep this site for reference for future problems. The manuals contain your complete gas burner specs and a how to service section to help you when it breaks again.

Regency Fireplace Products - Manuals (http://www.regency-fire.com/TechDocuments/Manuals/)

I change the thermopile in the one that wouldn't light - works great now - I changed the thermopile - thermocoupler - and thermostat in the other one with no success - the pilot light lights fine - when I turn the gas knob from pliot to on the burner lights up and stays lit regardless where the thermostat is? Any idea - could I have installed the coupler wrong?

The manuals were a great reference.

Disconnect thermostat wire and see if unit shuts off. If so then it is in the thermostat or associated wiring.

Does the fireplace have a bypass switch? I know most brands have some type of bypass that bypasses the wall thermostat and runs the fireplace continuous. Would be located near the gas valve.