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Question DetailsAsked on 11/15/2016

How could u tell if ur furnace control valve dont work

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Too many types of heating system control valves to answer your question definitively - if this does not answer your question correctly, repost more details about what valve you mean and your system type using the Answer This Question button right below your question.

Since you said FURNACE, not BOILER, I am going to assume you mean the gas control valve. To test that you need a Volt-Ohm-Meter (VOM) to check that it is getting the correct signal voltage from the control box, and through the thermocouple or thermopile at the pilot light. Generally - not always, but generally, if the pilot will light and stay lit, the gas control valve is not the problem - though there are exceptions.

Usually, if pilot will light and stay lit but burners will not come on, it is either the control knob is not fully turned to ON (or equivalent setting - sometimes just in a temperature selection range with some controls), or a safety sensor like a rollout or firebox overtemp sensor or an airflow sensor has malfunctioned or been tirggered - again, requires VOM to track down which it is, unless an electronic controlled furnace and it is giving you error code(s) or flashingor colored LED light pattern indicating what the problem is.

Can also be the controller itself - the unit the 120V cord/line goes into from the wall - but unless a seriosu electrical DIY that is not something to play with yourself. There are things you can check like sensor inputs and proper solenoid or relay action and proper voltages at right places, but again usually need VOM and the manual for that model.

If you have a thermocouple controlled pilot light and the thermocouple is more than a couple years old, or thermopile controlled and more than maybe 5-7 years old, that is commonly the issue - if so, pilot will light when the control knob on the gas control valve is turned to on and held in the LIGHT (or similar phrasing) position, but if it goes back out when you release it (after about 30 seconds holding it down/on till it warms up), usually the thermocouple is misplaced in the pilot flame, is worn out, or not making good contact - or with some models if the thermocouple lead is touching metal along the run it could be shorting out. [Is VERY low voltage so it shorting out does not damage rest of unit, just keeps the pilot and main burner gas from flowing except when start/light button is held down]

All in all gas control valves rarely die before the unit does - and in my experience their mode of failure is usually gas leakage, not failure to function, so that would normally be near my last thing to look at - assuming it is getting proper power to it when it is supposed to function.

IF this does not solve it but the assumption about it being a gas-fired forced air furnace was right, then a Heating and A/C contractor would be your normal Search the List category to find well-rated and reviewed companies to come look at it.

Answered 3 years ago by LCD

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