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gotoman for ac
gotoman for ac, HVAC Technician
Category: HVAC
Satisfied Customers: 5150
Experience:  51 years of experience install design and repair of all makes and models of AC
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I have an old Rheem RGAA 125c gas furnace which has been a

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I have an old Rheem RGAA 125c gas furnace which has been a reliable workhorse since the beginning. The wall thermostat has been flaky, and I've accessional needed to jump the red and gas flow terminals to get the heat on. That no longer works, so I replaced the wall thermostat with a new one. Unfortunately, the gas still won't come on. The pilot is fine.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I've always made sure the setting is notably higher than the ambient temperature when trying to start it. The filter is an ancient, washable, loose mesh, and is clean.
JA: Do you plan on doing the work yourself?
Customer: If I can. I'm comfortable with electrical work, but don't have a schematic for the furnace, so haven't tried troubleshooting the components there.
JA: Anything else we should know to help you best?
Customer: There are 2 cables fed to the wall thermostat, but only the four wire cable has ever been hooked up. I'm quite certain that the original installation was professionally done.

Russ here. If you jump the R and W terminals does furnace fire up. Do you have voltmeter. Russ

Customer: replied 4 months ago.
Jumping R & W was my go to with the old wall thermostat, but it no longer works, either with the old or new thermostat. I do have a meter, and I am getting 24VAC to the thermostat.
Customer: replied 4 months ago.
I haven't checked voltages at the furnace, as I don't have a schematic and some of the connections are in fairly tight spaces.

If you have 24 at thermostat and the touching the wires together do not work. Problem is at furnace. open switch or bad gas valve. Let me look I may have schematic.. Russ

Customer: replied 4 months ago.
I'm going out for the evening. I'll drop you a note when I'm online tomorrow, and you can connect whenever you're available.

No problem. I am having computer problems. Russ

Customer: replied 4 months ago.
Morning Russ,
I should be home all day today and will keep checking for messages.

Sound like igniter is bad. attached is manual and part numbers.

Customer: replied 4 months ago.
I don't find an ignitor in the parts list for my model/serial number. What does an ignitor do when there is already a pilot flame?The serial number on the unit is CN3D 107F 3577 5542

Standing pilot. OK Check voltage at gas valve. And also transformer to see if you have 24 volts. You should have 24 volts at thermostat R and W. Russ

Would help if you attached photo of gas valve assembly. Russ

Customer: replied 4 months ago.
I'm pretty certain that it's a stuck gas valve The valve is a 40 year old Robertshaw 7000BER with a copper flex bringing in the gas. From what I understand, the copper reacts with natural gas and over time will build up deposits in the valve. As I do have a full 24vAC to the valve when the thermostat is calling for heat, but get no gas flow, the valve would seem to be the culprit.

You got it good work. New furnace or new valve. Believe I would go with furnace. Russ

Anymore questions I am here. Russ

Do you need anymore help. Russ

gotoman for ac and other HVAC Specialists are ready to help you
Customer: replied 4 months ago.
Hi Russ,
Sorry for the slow response. I ordered a new valve from the parts list you sent, and installed it yesterday. All seems to be working fine. Thanks for all the help.