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Rick
Rick, HVAC Supervisor
Category: HVAC
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Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have an older wall furnace, it has a 24v supply to the gas

Resolved Question:

I have an older wall furnace, it has a 24v supply to the gas valve and a standard 30milliv pilot thermocouple. One day I found the pilot out. The pilot wouldn't stay lit so I replaced the thermocouple, still no good.

Looks like the 24v supply is out.

Looks like the furnace has been worked on in the past as the 24v supply housing says honeywell and the gas valve is white rogers model 3625 type 248

would the 24v supply being out cause the pilot to not stay lit?
I assume the 24 v n this case is AC or is it DC?
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Rick :

Welcome, my name is XXXXX XXXXX I will do my best to help you with your issue.

Rick :

The thermocouple is what tell the gas valve to keep the gas flowing to the pilot burner. If you have a 24 volt gas valve it's a thermocouple not a thermopile (although the there are a few rare exceptions

Rick :

Assuming only the top 1/3 of the tip of thermocouple is in the pilot flame and you have a good tight & dry connection at the gas control valve then the next most likely culprit is a faulty gas valve if the pilot won't stay lit when you release the pilot light button/dial on the gas valve. If the pilot is going out after you walk away then the pilot may be too weak and/or the pilot burner orifice may be dirty

Rick :

A draft is also always a possibility with a wall furnace

Customer:

You gave me some info but didn't answer any of my questions.

Rick :

The 24 volt control circuit has nothing to do with keeping the pilot lit

Rick :

It's 24 VAC

Customer:

Thanks, XXXXX XXXXX it seem coincidental that the gas valve stopped working and I'm not getting any voltage out of the transformer?

Rick :

The 24 volt circuit only opens the gas valve for the main burner. I can't say why the 2 things happened at the same time

Rick :

Even if you had no power to the unit the pilot should still stay lit with good thermocouple and gas valve

Customer:

Unfortunately you are pretty much confirming what I thought about how the gas valve works, I'm confident that the thermocouple is in properly. but still need to fix the power supply first

Customer:

crap I gotta stop hitting return more to come

Rick :

ok

Customer:

The gas valve says 24V 60cy .23 amp, does that mean I can use any power supply that puts out 24v AC and at least .23 amp or does it need to be exactly .23 amp output?

Rick :

You can use any 24 volt transformer. A 40 vA transformer is the most commonly used. The .23 amp designation just indicates how much power the valve draws

Rick :

Do you have a strong pilot?

Rick :

I suppose I should have said 24 VAC

Customer:

Yeah I even checked it with a multimeter and adjusted the flame till I got about 32 millivolts, still went out as soon as I let go of the button.

Rick :

Sounds like maybe a bad gas valve

Customer:

Do you have an online parts supplier you recommend?

Rick :

These guys have the best prices

http://www.pexsupply.com/

Rick :

But I have heard a few complaints mostly related to slow delivery when they didn't have something in stock

Customer:

Thanks, XXXXX XXXXX have them bookmarked, I'm gonna pay you now but how do I get back to you to continue troubleshooting if I need to, I'm gonna do the power supply first cause, the furnace won't work with out it, then continue on to the gas valve.

Rick :

You can just come back to this thread it won't go away. I'll answer related follow ups even after you rate me favorably

Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 14239
Experience: 40+ yrs. experience as a licensed oil & gas technician.
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