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Question DetailsAsked on 12/4/2016

Strong wind causes piolet light to go out on furnace

Propane furnace

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2 Answers


Assuming this is on-going and not related to low gas pressure because you are almost out of propane (in which case main burner flame would likely be erratic and subject to blowout also), here are some causes - in no particular order, just stream of thought:

1) If there is rust piled up around the pilot light bracket and thermocouple/thermopile, it can cool the thermopile or soak up the heat from the pilot flame, causing it to fail to generate enough voltage to keep the gas turned on when wind blows across it and cools it - make sure thereisno buildup around it.

2) ditto to the thermocouple/thermopile tip being properly immersed in the pilot falme - if the thermocouple has been changed and pulled back so there is less tip in the flame, that can result in excess cooling when the wind blows through the flue and shut the gas flow off. See manufacturer diagram on tip immersion in the bllue part of the flame (hottest part) - typically end 1/3 to 1/2 of the thermocouple/thermopile tip is supposed to be in the flame.

3) make sure any access panels/covers are properly in place, especially if a closed combustion chamber rather than open to the air

4) if you have independent ducted air supply to the furnace (usually sealed, not open air combustion chamber in that case), then make sure that ducting is not crimped, drooping, or frost flocked - which would inhibit incoming combustion airflow, hence accentuate the effect of exhaust flue pressure variations

5) you may need a windy area cap on the exhaust flue - commonly look something like one of these, with baffles and diverter to keep wind from blowing down the stack - the swiveling type works better but can cause severe blowback into the appliances if it rusts of freewzes in place, so I don't reocmmend them. The 360 degree symmetrical baffled ones work well in all but the strongest wind areas - biggest drawback to them is if your exhaust gas temp is real low, tend to frost up solid in moderate cold weather, especially if your units have standing pilot so always turning out moisture. Commonly the problem is around 10-20 degrees or so - cold enough so the metal is able to frost up fast, but not so cold that the furnace is running so frequently that it keeps the cap too warm to frost up. Can also frost up in extremely cold conditions, again more so with less hot exhaust gas (higher efficiency unit or long ducting to cap) - in extreme cases it is necessary to put rock wool insulation around the stickup ducting (including through the attic if unheated attic) surrounded by a third layer of galvanized or stainless ducting so the exhaust does not cool too much before reaching the cap.

6) check manual also on pilot flame - if it is not standing up straight and tall, typically about 1" of blue and blue/green flame is called for, it may be the gas flow to it is too low - there are adjustments on the gas control valve for the amount of gas going to the pilot flame. If at that point, usually better to have HVAC professional check it out.

7) sometimes, the pilot is located wrong relative to the main burner or the draft diverter is located wrong (the bent finger "finger" of shielding behind the flame), so draft through the exhaust vent and/or the main burner coming on can divert the pilot flame from the thermocouple/thermopile and let it cool down, causing the gas to shut off.

8) sometimes an older or failing thermocouple/thermopile can be barely generating enough power to keep the gas valve open - so because it is marginally operting, a bit of draft pulling the pilot flame away from the thermocouple tip a bit or even just blowing some cooling air across it can cause the gas valve to shut off because it thinks (due to the low power generation) that the pilot has gone out. Swapping out the thermocouple/ thermopile would solve the question of whether that is the cause or not.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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