I've got a century old house and at some point a floor heater was added. The heater is natural gas. It appears to have been retrofitted with a newer gas control valve that looks fairly new. It uses a pilot light and is controlled by a millivolt thermostat.

The problem is that the heater doesn't start up when the thermostat is triggered. I started by replacing the battery, and then the thermostat. I found that the heater will start if I short the wires together at the thermostat. So then I replaced the low voltage wire and cleaned the terminals on the control valve.

The heater started for about a week and then the old problem was back. I changed to a new thermostat again and still nothing.

I can't figure out why the heater will start if I short the wires together, but it won't when the thermostat is used. Any ideas?

 

say that if you jump out the tstat, and unit runs, tstat is bad. are you using a millivolt tstat, and what is the heat anticipator set on, and what is the amp draw of the gas valve?

 

I'm on my third thermostat in two weeks. It is a millivolt tstat. I don't know what a "heat anticipator" is and I don't know how to test the amp draw (although since it is an unpowered circuit, I'd say it ain't drawing much).