T-stat question on gas fire millivolt system

[MarkoPolo]

I am troubleshooting a problem with T-stat control of a Jotul gas fireplace. The unit is intermittently failing to light using T-stat control. When I toggle the mounted switch from”T-stat” to “On” the fireplace lights normally. I tried replacing the thermopile with no change. Occasionally the unit does respond to the T-stat so I thought the thermopile may have been faulty, but my thinking is probably flawed. . I have attached a picture of the block for reference. Red/white from thermopile, black/white from the 14\2 T-stat wire. Is it possible I just have bad T-stat? Can I easily test that? I have a basic Greenline multimeter…stove model number is
GF 200 DV II
Thanks.

 

[Fitter30]

Thermopile/ power pile same thing puts out 250 to 750 mv 1/4 to 3/4 volt.
Clean all electrical connections including the bare wire ends don't forget the thermostat . If thermostat has a open set of contacts take a piece of white typing paper small strip 1" long run it through the closed contacts twice. Gas valves will open with 190-200 mv

 

[Sponsor]

 

[MarkoPolo]

Thanks, it's definitely the Tstat. When I tap on it the fireplace lights, also crossing the wires at the Tstat lights it. Ordered a new millivolt Tstat.

 

[Mnalep]

Thermopile/ power pile same thing puts out 250 to 750 mv 1/4 to 3/4 volt.
Clean all electrical connections including the bare wire ends don't forget the thermostat . If thermostat has a open set of contacts take a piece of white typing paper small strip 1" long run it through the closed contacts twice. Gas valves will open with 190-200 mv

I am having an issue with burners coming on. I measured 187mv at TH to TH-PG with burners ON,, but a lot higher 633mv with burners OFF. Is the 190-200mv you mentioned with burners OFF, or ON. Thanks.

 

[Robert Gift]

Is the 190 to 200mA @ .25 to .75V not created by the pilot light flame? Whether ON or OFF should not matter.
After cleaning the.rmostat contacts well, if no improvement, short the wire from the.rmostat to see if the valve opens.

If not, I would reposition the thermopile in the hottest part of the pilot light flame to generate the most electricity.
If still not working, suspect something stuck in the gas valve. Withe valve removed I would gently tap it with a hammer while held in different orientations to get something fouling the valve or valve solenoid, out.
While tapping the valve I would also have a vacuum cleaner hose on the valve intake and outputo pull anything out.
Nextry a single 1.5-volt battery to try to gethe valve to open and close while vacuuming.
Write the manufacturer explaining what is happening and request another valve.

 

[Fitter30]

I am having an issue with burners coming on. I measured 187mv at TH to TH-PG with burners ON,, but a lot higher 633mv with burners OFF. Is the 190-200mv you mentioned with burners OFF, or ON. Thanks.

Agree with post 5 jump wires together at t stat.