I have a Superior by Lennox EPIC Free Standing Gas Stove. It was installed last January and is the primary heat source in our 130yr old farmhouse. I am having constant problems with the fireplace coming back on. I have tried 3 different millivolt stats, White Rogers Mercury Stat and HOneywell PRo 1000 1H and a 1H/1C. They all work the fireplace initially but once it falls below a certain temperature they are unable to make the fireplace turn back on. I need to turn the stat off and then on again to make it refire the fireplace. Crossing the stat wires makes the fireplace run but I want it to be able to turn on and off when called.

Any advice would be great.

Sometimes the wiring run is to long for a milivolt system to power. You have to remember that very little power is available and long wire length really adds to the problem. Many times the cheapest mechanical thermostat will work and on other fancy stats you need batterys and they still will not work due to resistance. How long is your wire run from the connection in the FP to the thermostat? It might be possible to hookup a 24 volt relay and a 120 volt to 24 volt transformer all hidden in the FP to allow the thermostats to work since your original thermostat control wires would then be very short. I actually hate using relays but sometimes you are forced to.

The stat wire run is no more than 25'. I don't care what kind of stat I use as long as it works.

As I mentioned a mechanical thermostat might work but it has to be a strait millivolt thermostat. Other types of thermostats have what is called a heat anticipator and those thermostats usually do not work with a millivolt system.

Check out the file below. You might check the thermostats you have tried to use and make sure they were set correctly for millivolt usage. Notice how the pointer goes to the rivet to eliminate the heat anticipator. You may have missed this setting when you installed the ones that did not work.