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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21829
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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My Lennox Whisperheat stopped producing gas heat, pilot

Customer Question

My Lennox Whisperheat stopped producing gas heat, pilot still lights and fan comes on. 10.8 volts are being delivered to M terminal on gas valve
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

If you only have 10.8 volts across M & C then follow those leads back to the ignition control and probe the terminals there. If the reading is the same then the ignition control is suspect. If you have 24 v at the control then you have a bad connection

Customer: replied 1 year ago.
the voltage was the same. The voltage from the P & C fluctuates also. So if I supply the M with 24 volts the valve should open ?
I had it working one day and the gas valve box was making a buzzing inside.
Expert:  Rick replied 1 year ago.

Yes 24 v at the valve and the valve should open. Valve could have been buzzing if the voltage was marginal

Customer: replied 1 year ago.
Does the 24 volts get delivered to the "Ignitor Control Module"? Should I measure incoming voltage there to determine if the transformer is bad ?
Expert:  Rick replied 1 year ago.

If the ignitor is arcing then you should have 24 v at the control but it wouldn't hurt to check across TR and GND on the control.

Customer: replied 1 year ago.
I only measured .1 volt at TR & ground there yesterday which didn't make sense as I thought that's the power line coming from the transformer and switching to the MV. Should the voltage at PV also be 24 volts ?
Expert:  Rick replied 1 year ago.

Only until the pilot is lit. Once it proves a pilot is present then voltage switches to MV

Expert:  Rick replied 1 year ago.

Also try across TH & TR

Customer: replied 1 year ago.
It never measured 24 volts either while igniting. With the leads unplugged from the gas valve the voltage wildly fluctuated
Expert:  Rick replied 1 year ago.

Could be a bad transformer or even a bad ground. I'd go back to the transformer and check voltage there. Should be constant 24v

Customer: replied 1 year ago.
Where on the transformer should I measure it? Should I trace the TR lead back to the transformer and measure it there? Also, is it best to check it out as it is normally installed or is it much easier to unscrew the bottom shield so I can access the transformer from above?
Expert:  Rick replied 1 year ago.

You would probe it at the connections closest to the transformer. This is an old unit and my recollection of how to access the transformer isn't very good.

Customer: replied 1 year ago.
Can I jumper 24volts to the main valve terminal of the gas valve to test the main valve's operation, or would this risk damaging the electrical components of the gas valve?
Customer: replied 1 year ago.
Is there only a sensor to determine the pilot lighting or is there one to determine the main furnace lighting as well?
Expert:  Rick replied 1 year ago.

As long as you remove the lead on the gas (main) valve it won't damage anything. Be sure the leads don't touch each other or anything else when you remove it. You have to leave the pilot valve connected or the pilot will go out and your jump won't cause the burners to light. The only way to do this is to use the transformer on the furnace. The sensor is in the pilot flame and as long as the pilot flame is lit the main valve should open. There is no sensor for the main burner(s).

Customer: replied 1 year ago.
I found that the transformer is only putting out .18 volts. On the side it says 30VA blue-yellow, which is the color wires going to the main board. To get a replacement transformer, should I look for that voltage or a 24v output, which is listed on the schematic ?
Also how many amps should it be? It's not listed on the side. I could provide a picture of it if that would help.
Is there any reason I shouldn't replace it with any old transformer that outputs the required volts & amps?
Expert:  Rick replied 1 year ago.

You need a 24 volt 40 VA transformer. A 40 VA is pretty common.
I'd appreciate a favorable rating

Customer: replied 1 year ago.
Everything still operates except for the main gas valve even with this low output reading on the transformer, how can this be?, it doesn't make sense to me...
Expert:  Rick replied 1 year ago.

Did you replace the transformer?

Customer: replied 1 year ago.
I replaced the transformer but it reads less than 1 volt too. I even wired it straight to the wall and it reads the same thing. It looks brand new. Does it need any equipment hooked up to it to turn on and produce 24 volts?
Customer: replied 1 year ago.
It's should produce 24volts DC right? I'm scratching my head how the original and the replacement transformer are showing the same readings.
Expert:  Rick replied 1 year ago.

What is the voltage on the primary side of the transformer?

Customer: replied 1 year ago.
123 volts ac from the board. 119 volts from the outlet at my other place going into the new transformer.
Expert:  Rick replied 1 year ago.

Then if you have ~120 volts on the primary and 1 volt on the secondary and this is a 24 volt transformer then the transformer is faulty.