Jotul Cuts In and Out

[jfm]

I just moved into a house that has a Jotul GF 300 DV running on propane. When I turn the Burner switch to the ON position it comes to life, but then it cuts out after about 30 minutes. It then turns back on after another 30 minutes, and the cycle repeats. When the burner is first turned on the flame is a little low - even on the High setting, but it seems to get higher the longer it is on until about 30 minutes, when it quickly goes lower and lower until it finally cuts out. The pilot stays on the whole time.

I have a little bit of an electrical background, so I made some measurements on the thermopile. With just the pilot on it reads 556mV. When the Burner switch is turned on the voltage immediately drops to 236mV, and then drops a little slower down to 175mV over the next minute. The voltage then stays in the upper 170's to lower 180's until the burner cuts out after about 30 minutes, at which time the voltage rises at an average of 1.75mV per minute until the burner turns back on at about 233mV. The cycle then repeats.

What could be the problem? I would appreciate any comments.

 

[DAKSY]

Replace the thermopile. You can probably get a universal millivolt generator at a True Value. $50+/-

 

[jfm]

Thanks for the feedback. What voltages should I be reading with the pilot on and with the burner on?

 

[DAKSY]

Most thermopiles are 750mV components. I try set them at 550mV engulfed in the pilot flame.
You may or may not be able to hit that number exactly, but +/- 30mV will work fine.
Too high (600mV+) & you will smoke the t-pile.
Once you hit the switch, the reading will drop to around 250mV.
That's fine. I try to make sure they're over 200mV with the burner running.
All readings should be taken with the glass front on the unit.

 

[Heatsource]

what kind of valve is in this stove?
i can post some valve tech specs for testing...

 

[jfm]

So it seems that my pilot is set correctly with a reading of 556mV, but the thermopile is weak because it drops below 200mV while the burner is on. And the low voltage cannot keep the valve engaged. Is this correct?

 

[jfm]

I cannot read the label on the valve without taking it out of the unit, but it appears to be a SIT 820 from the pictures I have seen online.

 

[DAKSY]

So it seems that my pilot is set correctly with a reading of 556mV, but the thermopile is weak because it drops below 200mV while the burner is on. And the low voltage cannot keep the valve engaged. Is this correct?

Yep. The millivolts required to hold the magnets open is drawing more than the t-pile can generate. Replace it & you'll be fine.

 

[Heatsource]

http://www.montigo.com/files/manuals/archive/XP0121 Service-Technical Guide_Part-1_041108.pdf

^ here is a nice service guide!

 

[jfm]

Yep. The millivolts required to hold the magnets open is drawing more than the t-pile can generate. Replace it & you'll be fine.

Well, I replaced the thermopile with a new one and still have the exact same problem. In fact, the voltages measured at various stages are almost identical with the new and old unit. Any idea where to go from here?

 

[DAKSY]

Jump the TH-TP & TH terminals with the switch off. Does it still exhibit the symptoms?

 

[jfm]

Jump the TH-TP & TH terminals with the switch off. Does it still exhibit the symptoms?

Same result. What does jumping those terminals do?

 

[DAKSY]

Takes the place of the switch or t-stat.
What you did was eliminate the on-off rocker switch as the source of the problem...
Time to start looking at the rest of the wiring.
Something is drawing millivolts off that t-pile.
Did you read the info that Dave Gault posted up above?

 

[jfm]

Takes the place of the switch or t-stat.
What you did was eliminate the on-off rocker switch as the source of the problem...
Time to start looking at the rest of the wiring.
Something is drawing millivolts off that t-pile.
Did you read the info that Dave Gault posted up above?

I have just started to go through the service guide, and it looks like there are some tests that I can perform. I will begin to go through these and report back.

 

[49er]

I don't know if this would even be possible with a residential system but I'm wondering if your regulator at the tank or some other part of the supply is icing up and blocking the gas flow?
I only mention this because we have a patio heater that uses the 20lb BBQ cylinders and it used to do nearly the same thing. It would start out fine and then the flame would go real low after an hour or so and the regulator would be covered with frost. It wouldn't work right again until I turned the heater off and let it defrost for awhile.

Anyways, just another thought.