Heat only millivolt non-programmable thermostat stops turning propane stove on after 20 years. Stove turns on/off just fine using manual switch in back of stove. So I assume thermostat bad and replace with another millivolt unit. New unit turns stove on just fine, stove runs fine, reaches temperature, then turns off. Now thermostat will not turn stove on no matter what. Manufacturer says it is bad, I get replacement and it does exactly same thing. Turns stove on once, turns it off, then nothing. Checking thermostats, they are operating fine and closing circuit even after thermostat fails to start stove. Wires are just fine, thermostat about 30' from stove, stove operates as it should with manual switch. Checked all connections and tightened. Shorting the two wires — usually — turns stove on but not always. When thermostat won't start stove, shorting wires will not start stove. Stove manual switch works just fine and is closing same circuit in stove?? Obviously something weird, probably has to do with the millivolt generator (pilot light always works fine – no problem) or the thermocouple. Stove dealer scratching head. Anyone have a solution or idea as to what it could be? Maybe millivolt generator putting out too low voltage? I haven't measured that but thermostat turning stove on and off once and then not anymore after that would not make sense. Thanks for any suggestions.
Problem controlling propane free-standing stove with a millivolt thermostat
heatingthermostat
Related Solutions
Looking at your thermostat specs etc, I assume it is a basic bimetallic rotary spring operated mechanism with manual SPST switching. since you can operate it to "on" and you know the contacts close in manual mode, and when physically turned/twisted, I suggest a couple of tests to verify operation of the bi metal spring. Disconnect the electrical power. Use an air heat gun to blow on the sensor unit and watch to see if actuator moves in the switch housing as you would expect. Connect an Ohm meter across the load/fan terminals. As the temp rises, the ohms should change from infinite/open to 0 ohms/closed when contacts close at the set limit. Although this is not a calibrated test, it will verify that the spring is responding to temp changes. If this test works properly and you are satisfied the unit is working, I may suggest you look at where you are trying to sense the heat from the wood stove. It may be that the area you have selected to mount the thermostat is not seeing enough heat from the stove. you may have to monitor the temp closer to the flue or at an area that radiates heat better. You may also have to fabricate some type of small plenum directly on the surface of the stove for the sensor to mount into. In that I mean just the spring/temp sensor assembly, not the actual electrical switch assembly. Good luck.
You'll need a transformer to step down mains voltage, to 24 volts that the thermostat can use. And you'll need a relay that can work with 24 volts.
You'll wire it up something like this.
When the thermostat calls for heat, the relay contact will be pulled closed. This will signal the fireplace to turn on.
NOTE: the three contacts used on the thermostat are R, W, and C. In the drawing the C may or may not look like a C, so I just wanted to make that clear.
Related Topic
- Replacing a Honeywell Thermostat with a remote thermostat
- Help with smart thermostat wiring
- Electrical – Electric baseboard heaters stuck on with digital thermostat
- Electrical – Why the baseboard heater won’t turn with new thermostat
- Wiring – How should the thermostat wires be connected to the furnace
- Millivolt fireplace turns on by the thermostat but will not shutoff
Best Answer
That might indicate a thermocouple problem. The thermocouple makes the electricity which the millivolt thermostat is turning on and off. That electricity opens the gas valve.
Oh, well, then. If that manual switch is directly operating the gas, that still points to thermocouple.
If it electrically shorts the wires (as the thermostat does), then that would seem to exclude the thermocouple. That would point to the wiring in the walls, and 99% of the time, a "wiring in the walls" problem is actually a "loose/corroded/faulty terminal connection".