Press down the Pilot Light button setting to keep the pilot light lit
for half a minute or more. The thremocouple has to be warmed up
before it will generate a strong enough signal to keep the gas valve
open. Once the pilot light stays on turn the gas valve setting to ON.
The last time I had the problem was years ago and can't remember too
much else. Since you said the furnace did light once then the
equipment is probably OK. The remaining suggestion is to see if the
pilot light is always directed on the tip of the thermocouple. My dim
memory of the last fix was that I had to fiddle with the thermocouple
mount (adjust mounting screw, bend the clip??) to bring the tip onto
the hottest part of the pilot light flame, the part just above the
blue cone as per high school lab description. Also use steelwool or
emery paper to clean the soot off the tip of the thermocouple. Soot
is heat insulating and may give a false reading. Maybe clean up the
original thermocouple and try relighting with that.
My house is 25 years old and at the time of its construction we had to
(new rule) put in an independent air source for the furnace combustion
air. I made a box duct to channel the outside air source direct to
the combustion inlet as an open duct from the outside was pouring very
cold air into the basement. Most people just stuffed up the pipe with
insulation. During high winds the gusts would blow out pilot light. I
placed a small sheet of metal to act as a baffle between the box duct
outlet and the pilot light. Works like a charm and that's for more
than 10 years by now.
Do not discount the possibility that the gas control valve may be faulty.
Last year I went through about 10 or so thermocouples before i just got sick
of replacing thermocouples and changed the gas control valve...... to an
auto-ignition intermittent pilot system (very nice).
This is Turtle.
Sounds like the Gas valve being bad but you can have a problem where the
thermocouple screws down into the valve. There maybe two wires coming to the
point where the thermocouple into the valve at and these two wires goes to a
shut down on the furnace where the go to the furnace wall. these is a shut down
switch at this point and can be the problem. Check it out.
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