Stove Doesn’t Always Turn On with Thermostat

[Dieseltruck15]

I have a Lopi Berkshire hooked up to a thermostat. Every now and then (it’s been happening more often), when the thermostat calls for heat, the stove won’t ignite. The pilot is lit, but the main burner never fires. I at first thought it was the thermostat, so I changed that out and it still is doing it. Again, it’s not all the time, it may only happen once a week. To get the stove to actually fire, I have to shut the thermostat on/off sometimes once and sometimes a few different times to get it to light. Was wondering if someone can point me in what direction to look?

Thanks!

 

[DAKSY]

Disconnect the wiring from the t-stat.
Touch the two wires together.
If the unit comes on immediately, the problem is with the t-stat.
If it doesn't the problem is in the wiring, whether it's compromised,
or connected improperly to the terminal block on the valve.

 

[Dieseltruck15]

I’ve tried 2 separate thermostats and it has happened on both of them, so I don’t believe it’s the thermostat. It only happens every so often, maybe once a week, so I don’t believe it is in the wiring either.

Could a failing thermopile cause this issue? What should the thermopile be putting out for voltage?

Thanks

 

[DAKSY]

A bad TP is possible. With the burner off, most units will have a millivolt reading of 525+/- 25 mV.
When the burner is turned on, the reading will drop to about 225+/- 25 mV.

 

[DAKSY]

Did you try jumping the tstat wires, just for the heck of it?

 

[Dieseltruck15]

I haven’t tried jumping the thermostat wires recently. I did back awhile ago and it kicked on each time.

With the burner off, I have 429 mV on the thermopile. I haven’t tested it with the burner on yet.

Thanks

 

[DAKSY]

429mV is WAY low. If you take 300 from that when the burner is actuated,
your mV will barely be enough to keep the gas flow going...
Can you adjust the pilot?

 

[Dieseltruck15]

I checked the voltage on the thermopile with the burner on after it had been running for awhile, it was 250 mV. I checked it a couple minutes later (burner was still on) it was then at 307 mV.

Once the burner kicked off when it was up to temp, it was at 420 mV but only for a few seconds then it started dropping down. After a couple minutes it was down to 370 mV but it was then starting to slowly climb back upwards.

Should I try seeing if there is any build up on the thermopile or is this a normal range for the thermopile?

Thanks

 

[DAKSY]

You can try to clean it, but my bet is that the TP is on it's way out.
True Value sells universal millivolt generators for around $50...

 

[Dieseltruck15]

There is an adjustment screw for the pilot but I think it is close to open all the way, I’ll have to double check it though. I try to keep it with blue flames off the pilot and not yellow, isn’t that correct?

I’ll probably swing over to my local hardware store and get a thermopile just Incase.

 

[DAKSY]

You need to get as much flame on the top 3/8" of the
TP as you can without overheating it.
550mV is a good number to shoot for.
Over 600mV can lead to premature failure.

 

[Fingerlakes Fireplace]

With the burner on, as long as you have a minimum of 125 mv the burner will come on. New thermopiles, with the burner on as a load, will run anywhere from 250 to 325 mv.
Keep in mind that you have to have a millivolt thermostat!
Some non millivolt thermostats will work for a little, and some not at all.
If you take the wires off at the stove going to the thermostat, and do an ohm reading, the value will tell you if it is the wires and or thermostat. I like to see the resistance under .3 ohms.
If you have a very good thermopile, up to 1 ohm resistance will still work, but you will have problems down the road when you're thermopile gets weaker.