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.