Furnace will not come on all the time

Old 01-22-13, 02:55 PM
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Furnace will not come on all the time

Hope you can help.. First off, let me say I know my furnace is old, but not in the budget this year to replace..I am hoping to keep it going this year and budgeting a new furnace for next year...so that is why I am here.. don't laugh, but I have a williamson tempomatic. Natural gas. Problem I am having is it may work for days, then when the temperature drops below the setting on the thermostat, I hear a click but heater does not kick on. I go down to the basement, pilot light is lit. I have attached a picture of the part that I lightly tap with a screwdriver and all of a sudden the furnace fires up. It is the part in the picture that has pilot duty rating on it. Is this a relay? With the age of the furnace is there a chance this is bad and what are the chances of finding a replacement. Anyway with the pilot light kicked in all the way, I go up to the thermostat, turn it to the off position, then turn it to heat. if heater does not kick on in a minute or so, I turn the thermostat to off postion, and then back to heat, and usually withing a few seconds it kicks on..Any ideas? PLEASE.. Woke up this morning to house at 55 degrees.
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Old 01-22-13, 03:35 PM
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That looks like the gas valve you are tapping on.

Is there a model number listed on that hi mileage beauty
There may be a part number listed on the valve too.
Old 01-22-13, 04:02 PM
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Your picture is of a very old school mercury flame sensor.

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Old 01-22-13, 05:46 PM
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This mercury flame sensor system probably dates from the 1970s.

The pilot flame must engulf the flame sensor which should sit in the pilot flame. The heat of the pilot flame causes the mercury in the sensor to vaporize, which causes a pressure spike in the capilary tubing which turns on the main burner at the electric gas valve.

The odds are good that that the pilot burner and pilot orifice are dirty and need to be cleaned to provide sufficient heat to cause the flame sensing system to turn on the main burner.

The pilot burner needs to be disassembled and the pilot orifice and pilot burner cleaned. The pilot orifice is at the end of the pilot tubing, held into the pilot burner by a brass fitting that needs to be loosened with a wrench so that the pilot tubing can be pulled out of the pilot burner, which provides access to the pilot orifice for cleaning.

Try that and the odds are pretty good that you will be back in business.

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