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Re: furnace pilot light

Posted By: AHandyman
Thursday, 5 November 1998, at 6:57 a.m.

In Response To: furnace pilot light (Bob)

Bob,

An old standard furnace with a standing pilot and thermocouple is pretty straight forward. If the thermocouple is good, and the flame stays in contact, the millivolts provided by the heat will hold in the selinoid valve that allows for furnace operation. If it is this type and the thermocouple is good, it is possible that the selinoid that the thermocouple attaches to is weak. Those are sometimes replaceable and sometimes a new main valve needs to be installed. The only effect air flow can have is if there is a "breeze" somewhere that is blowing the flame away from the thermocouple. (maybe a hole in the heat exchanger in such a place where the furnace fan coming on causes this.. or a leak in the cabinet surrounding the heat exchanger..)

At any rate the older standing pilots or even ignition types that still use a thermocouple are pretty straight forward.

Newer high effeciencies tend to use a flame sensor that acts more quickly than a thermocouple. In that case the flame sensor and or pilot assy may need replacement. Those ususally lead back to a printed curcuit board that may be bad.

In the case of the flame sensor, it is ususally more suseptable to the flame not being in contact because it is faster acting. If the flame isn't in contact due to a "breeze" it will pretty much shut down the furnace immediately on lack of proven flame..

Hope that helps!

Don

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