Gas furnace problems


Old 10-22-11, 07:20 AM
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Gas furnace problems

I have a Ruud UGDA-125A-GR forced air gas furnace that is not working. The fan comes on when switched on and the AC does as well. I removed the elctronic thermostat and direct wired the red common wire and the white heat wire and nothing happens. Pilot light is lit. I jumpered across the the red and white terminals on the furnace and nothing happens. I've measured the voltage acroos the red and white terminal and get 44-V instead of 25-V. The furnace has fired twice in the last 24-hrs. It came on for a short time and then shutdown before reaching the temperature setpoint each time. Any ideas?
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Old 10-22-11, 07:29 AM
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how good of a meter are you using? Check for a open limit or rollout device that is in the gas valve circuit.
Old 10-22-11, 09:34 AM
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Connect one terminal of your voltmeter to the C terminal and set the meter to measure ac voltage of 30 volts or more.

You should get about 24 volts AC when the door switch is closed, and 24 volts at the W terminal when the thermostat calls for heat.

Trace out the voltage through the limit switch and other switches to the gas valve and report what you find.

This is called "walking the circuit" and is a widely used diagnostic method.
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