DuoTherm Gravity Heater w/ millivolt... having problems - Fiberglass RV

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Old 10-05-2014, 04:33 PM   #1
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Name: Mountain
Trailer: 1976 Coachmen Cadet
New York
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Unhappy DuoTherm Gravity Heater w/ millivolt... having problems

Hello Everyone!

This is my first post here, although I have been looking around for some time now to help troubleshoot my issue here... (I hope im posting in the right spot here)

I have a Duo Therm gravity heater that was working last year, but refuses to work correctly this year (it did have some trouble last year). This heater has millivolt generator.

Last year, I would have to turn the pilot ON when the thermostat was ON, so that a quick whoosh of gas (that only comes out when the operator knob is turned from PILOT to ON) would instantly light the burner. (everything worked fine from there on out. it would start, turn-off and re-start with no problems)

This year, (with the thermostat on) no matter how long I hold the pilot in, I cannot turn the operator knob from PILOT to ON.

I can get the pilot to light,,.. as long as the thermostat is set to OFF. (this is how you are supposed to do it per the instructions). I turn the operator knob from PILOT to ON. that the pilot is on, I turn the thermostat ON, and there is a loud CLICK/Bonk noise. I believe this is the Thermo-magnet safety valve shutting closed. (the instructions state that a safety valve will close when the pilot burns low, goes out, or becomes unstable.

I did get the pilot to turn ON with the thermostat ON a few times this year. One time it seemed to be burning low, and the flames were yellow.

This made me think that there is not enough oxygen.

I cleaned a bees nest out of the exhaust already, (i thought this was the problem originally, as i got it to light up afterwards) and have attemped to clean the air intake with a plumbing snake, (although i cannot see where the tube connects to on the inside of the flame box, so i cannot be sure that it is clear)

Any thoughts on what else i can check? I feel as thought the Thermophile is working because I can get the Pilot to stay ON when the thermostat is OFF. But for some reason, as soon as I turn thermostat ON, the pilot will not turn ON.
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Old 10-05-2014, 04:41 PM   #2
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Name: Mountain
Trailer: 1976 Coachmen Cadet
New York
Posts: 3
Also, I thought that perhaps the digital Thermostat that I was using could be the problem, (even though it worked last year). So I went out and bought a new digital thermostat that definitley works with millivolt, and I am still having the same problem.

I also thought that perhaps I have the wiring wrong on the operator (even though it was how I left it last year) and I cannot find wiring instructions anywhere. it has 4 wiring connectors, 2 for the millivolt Generator, and 2 for the Thermostat. They are joined by a jumper in the middle.



^ I have it wired as such

thanks again!
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Old 10-06-2014, 11:21 AM   #3
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Name: Mountain
Trailer: 1976 Coachmen Cadet
New York
Posts: 3
just some hard facts about this heater.. it is a 65515-003. 003 meaning it has the B67 Midgitrol Combination Gas Valve. mine is wired using the PG9 Millivolt Generator

EDIT: UPDATE: 4pm.Oct.6.2014

I have tested the Operator contacts with a millivoltmeter as instructed in the manual. This requires that the Pilot be ON and the Thermostat CLOSED or ON. I can only accomplish this by holding in the Pilot light.

The readings I obtained show 105mV across the PG9 thermophile millivolt Generator. The manual says that this reading should be greater than 140mV.

When I tested the Generator with the Thermostat OPEN or OFF I received a reading of 215mV. If the required millivoltage for the operator is around 140mV, This would explain why I can get the Pilot ON when the Thermostat is OFF. Turning the Thermostat ON causes a drop in millivoltage that causes the thermomagnet safety valve to close.

The manual states that I should clean the Pilot burner orifice and primary air holes.

ill update again later
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003, 65515, b67 midgitrol, digital thermostat, duo therm, duo-therm, duotherm, gravity, gravity furnace, gravity heater, honeywell, millivolt, pg9 generator, thermomagnet

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