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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 19555
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have Larrs model LG-259-N-C, the gas valve does not open.

Customer Question

I have Larrs model LG-259-N-C, the gas valve does not open. I have checked the different limit switches and all seem to be operating properly. I have changed out the signal generator and have 350 millivolts output. Is this enough to open the main gas valve? Is there something else I can check?
Submitted: 4 months ago.
Category: HVAC
Expert:  Rick replied 4 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.
When you refer to a signal generator do you mean the thermopile in the pilot flame? Do you have a strong pilot flame?

Customer: replied 4 months ago.
I have a strong pilot flame and yes I mean the thermopile in the pilot flame.
Expert:  Rick replied 4 months ago.

OK, 350mV is borderline (depending if you are metering with the leads attached) but should be adequate. Try jumping TH & THTP on the gas control valve. Does the burner fire up?

Customer: replied 4 months ago.
Thank you I will that.
Expert:  Rick replied 4 months ago.

You're welcome, if it fires up then you have an open switch somewhere in the control circuit. You can try jumping them out one at a time.

Customer: replied 4 months ago.
That did not work, I have checked all my switches with an ohm meter and they are closed.
Expert:  Rick replied 4 months ago.

If you have 350 mV from the thermopile and you jump TH & THTP and the burner doesn't fire up then you have a bad gas valve. I'm assuming thermopile is connected to TP & THTP .

Customer: replied 4 months ago.
Is there a coil that can be changed out or must I order the complete valve.
Expert:  Rick replied 4 months ago.

You can't repair the valve it must be replaced.

Customer: replied 4 months ago.
Thank you
Expert:  Rick replied 4 months ago.

You're welcome!

Expert:  Rick replied 4 months ago.

I'd appreciate a favorable rating