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I have a propane fireplace that wouldn't start. Cleaned the thermopile and thermocouple and got the pilot to work fine. Then the main burner wouldn't light from the thermostat--it only lit if I jumped the terminals at the fireplace with a paperclip. Then it ran. I could turn it OFF from the thermostat, but not back ON. So I removed the thermostat, connected the wires -- that would turn the thermostat both off and on. So I replaced the thermostat, and still have the same problem-- the thermostat turns the burner off but not on.

So what's my problem? Is the thermopile or thermocoupler bad? Is there another bad switch in the circuit somewhere?

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    How far away from the fireplace is the thermostat located? Are all of the wiring connections tight? Is the thermostat rated for pilot duty or millivolt duty? What wire gauge is run between the fireplace and the t-stat? I suspect the pilot generator is getting weak. You can check it. It should be putting out a good 700 to 800 mV, 500 to 600 is not enough. – Paul Logan Dec 7 '17 at 4:30
  • Thanks Paul. The thermostat is across the room--a good thirty feet of wire away. It is a millivolt thermostat. Not sure on the wire gauge--it is solid copper but thin, like for a doorbell. I am getting more like 380mv between the tp and tp/th terminals at the fireplace. When you say pilot generator--are you talking the thermopile? It has a thermopile and a thermocouple, with a good flame on both. – tony s Dec 7 '17 at 22:03
  • Yes what you called a thermopile I called a pilot generator. The thermocouple maintains the pilot flame. The thermopile generates the power to hold the main gas valve open for the main flame. It is especially important on these systems, because the voltage is so low that all electrical connections be clean and tight. Are you getting that voltage with the main flame going or just the pilot flame only? What is your history with this appliance? Has it worked for you properly in the past? – Paul Logan Dec 9 '17 at 4:59
  • I went to jump it and touch the wire with my hand - and it went on. further investigation showed that one of the wire connectors to the thermostat was loose. took the connector apart, bent it tighter with a pliers, and voila! it worked. Thanks so much for your help! – tony s Dec 17 '17 at 20:59

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