Vermont Castings pilot problem

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wooduser

Minister of Fire
Nov 12, 2018
679
seattle, wa
Unfortunately, that indicates a bad electric gas valve.

650 millivolts is actually more voltage than you ought to have. That suggests that the pilot valve electromagnet that holds the pilot gas on when you quit holding the valve open is bad, the circuit is open, not using the millivolts it should to energize the electromagnet..

You can check the resistance between TP and TH/TP ---- you'll likely find that an open circuit when the circuit needs to be complete to energize the magnet.

The millivolts drop when the switch is turned on because they are being consumed by the main burner gas valve solenoid when it is energized.

I recommend against DIY replacement of the gas valve. It's just more than a do it yourselfer should take on, and the main burner gas pressure needs to be set when the new valve is installed. That's my bias, anyway.

You might want to make a note of the make and model of the electric gas valve when you are shopping for service. A repairman ought to be able to bring a suitable replacement valve with him with that information.

Sorry this wasn't a simpler repair. A bad spill switch or bad thermopile would have been good DIY repairs, and much more common than needing to replace the electric gas valve.
 

Vermont Mike

New Member
Dec 3, 2018
15
Ontario, Canada
Unfortunately, that indicates a bad electric gas valve.

650 millivolts is actually more voltage than you ought to have. That suggests that the pilot valve electromagnet that holds the pilot gas on when you quit holding the valve open is bad, the circuit is open, not using the millivolts it should to energize the electromagnet..

You can check the resistance between TP and TH/TP ---- you'll likely find that an open circuit when the circuit needs to be complete to energize the magnet.

The millivolts drop when the switch is turned on because they are being consumed by the main burner gas valve solenoid when it is energized.

I recommend against DIY replacement of the gas valve. It's just more than a do it yourselfer should take on, and the main burner gas pressure needs to be set when the new valve is installed. That's my bias, anyway.

You might want to make a note of the make and model of the electric gas valve when you are shopping for service. A repairman ought to be able to bring a suitable replacement valve with him with that information.

Sorry this wasn't a simpler repair. A bad spill switch or bad thermopile would have been good DIY repairs, and much more common than needing to replace the electric gas valve.
 

Vermont Mike

New Member
Dec 3, 2018
15
Ontario, Canada
Double dam.

I don’t mind calling in a pro. I’ll check the gas valve part number. My concern is getting someone that can deal with an old piece and fix it successfully.

Wish me luck. Thanks for all your help. I’ll let you all know how it works out.

Thanks, Mike
 

Vermont Mike

New Member
Dec 3, 2018
15
Ontario, Canada
No, thanks for your time Wooduser.

Ok. I’m using the TOP and CENTER screw connection points(as shown in picture a few posts back) I get:

650 mv with pilot on and main burner switch OFF

250 mv with pilot on and main burner switch ON

I’ll probably install the thermopile when it gets here.

Check some continuities and voltages. Keep plugging away.
 

wooduser

Minister of Fire
Nov 12, 2018
679
seattle, wa
I’ll probably install the thermopile when it gets here.

Check some continuities and voltages. Keep plugging away.


What I'd do to verify my conclusion is to disconnect the black wire with the clip on the end, which is the w wire leading to the pilot valve magnet. Check the resistance in ohms from that wire to chassis ground. If the magnet is good, you ought to get a resistance of several ohms. If the magnet wire is burned out or broken as I suspect, it would be an open circuit.

I'd pull the wire clip off so you are measuring directly to the wire and have noting else attached to the circuit.
 

Millbilly

Feeling the Heat
Dec 13, 2015
291
02648
I just reread this thread and think you might have gotten bad information. I'm not exactly sure how this is wired without looking at it. A lot of older stoves are not necessarily wired how the manual says. That being said I still think it could be the spill switch. Someone else instructed you to disconnect it.. no no no. You need to Jump it. The spill switch is a bimetalic switch that is typically closed, it opens when too hot. So you need to disconnect the wires from the switch and then connect them to eachother.
Next if the burner does not turn on you need to check the pressure on the P out port. If you are getting pressure then you need to check for burner line/orifice obstructions.
If you are jumping the spill, the switch is dropping your mvs from 600 to 250, and you have 0 pressure out, then I'm fairly certain you have a bad valve. You can to that resistance test to confirm.
 

wooduser

Minister of Fire
Nov 12, 2018
679
seattle, wa
That being said I still think it could be the spill switch. Someone else instructed you to disconnect it.. no no no. You need to Jump it. The spill switch is a bimetalic switch that is typically closed, it opens when too hot. So you need to disconnect the wires from the switch and then connect them to eachother.



I was presuming that the spill switch was normally open and if it closed shorted to ground. I find that a common arrangement. But Millbilly is quite correct, what he describes is an equally possible way to wire the switch.

If there is only one wire going back to the spill switch, with the other side of the switch grounded to the fireplace sheet metal, the testing method I suggested, disconnecting the wire to the switch, is good.

If you find two wires going back to the spill switch, then Millbilly's method would be the one to use, and connecting a jumper wire across the switch to eliminate it electrically and then checking to see if the pilot stays lit would be the way to test it.

Sorry my answer wasn't more complete. I should have included Millbilly's test as well.
 

wooduser

Minister of Fire
Nov 12, 2018
679
seattle, wa
Next if the burner does not turn on you need to check the pressure on the P out port. If you are getting pressure then you need to check for burner line/orifice obstructions.


I'm not clear on what you are suggesting here, Millbilly. As I understand it, Vermont Mikle is getting gas to the pilot burner which lights OK but doesn't stay lit after giving the thermopile time to heat up. If that's the condition, I don't see a reason to test the pilot gas pressure.o main burner gas pressure.