The thermocouple was used to hold the pilot valve open. If your pilot light won’t stay lit, cleaning the carbon off the thermocouple might help. Issue #1: Bad thermocouple A furnace thermocouple is a safety feature that regulates gas flow to your system based on whether or not the pilot light is on. 1. The pilot can go out for a number of other reasons, however, so if you're having trouble getting the pilot to stay lit , the thermocouple may not be at fault. It does this by sending a tiny electric current to a sensor on the gas valve signaling the valve to stay open. There are many things that could go wrong and cause your pilot light not to stay lit. Tested for power at the transformer--OK. They are dependent on one another, totally. After years of use, your thermocouple may have a buildup of carbon deposit, which affects its ability to function. Replaced the thermocouple--same result. Its not putting enough voltage through to the valve to tell it its lit. If my Thermocouple is bad will my pilot light stay lite. Forced air furnace who's pilot won't stay lit, not the thermocouple [ 1 Answers ] Pilot won't stay lit beyond releasing the button to light it. It consists of a heat sensor connected to a solenoid; when the sensor is not heated by the pilot flame, the solenoid closes the gas supply line. Seattle Pioneer: This unit is a standing pilot. The thermocouple can do this because, in its probe, it contains two different metals, and a … If the pilot is staying lit but the burners won't light the thermocouple is likely toast. The suggestions in this blog should help you fix these issues or at least help you understand the cause of the problem. Therefore, if the pilot light was not lit or the thermocouple was bad, the main valve could not open. Will pilot stay lit if thermocouple is bad? 45 year old Pioneer heater. Pilot does not light or stay lit after knob is released - Check carefully that gas to appliance is on and that the valve is in the correct (pilot) position and fully depressed when lighting. According to the check list posted on the unit, it says that if the thermocouple has been changed and the pilot light will not remian lit, the next item is the valve body. When a thermocouple fails, the pilot light won't stay … The usual suspects, however, are the thermocouple, pilot tube, flex tube, and main control valve. If pilot ignites but does not stay lit after knob is released, then the problem is with the thermocouple not generating enough voltage to the valve. Everything looks good and I too think it could be the gas valve that is gone bad. Replace it with something made this century. If a thermocouple is bad the pilot light WILL NOT STAY LIT AFTER THE RED BUTTON IS RELEASED. It’s designed to determine whether the pilot light is lit and then subsequently signals the gas valve to open. 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