So you have found the pilot light will not stay lit when you try to light the pilot light. You know you have gas and everything seems to be fine so what is the problem? You ask a friend and the friend tells you the thermocouple is bad. So how do you test the thermocouple to see if it is bad or not? You will need a multi-meter that will read millivolts (most meters read small voltage like millivolts which is 1/1000th of a volt) and a source of fire such as a lighter or small torch.
- Remove the thermocouple.
- Turn on the meter and set it to Ohms. Touch the two leads together from the meter and you should get a reading close to zero. With the leads apart you will read infinity.
- Start the flame and put the tip of the thermocouple in the fire.
- Ensuring the tip is nice and hot from the flame take one lead from the meter and put it on the shaft of the thermocouple and the other lead and put on the end of the thermocouple where it makes contact with the gas valve.
- If the reading is less than 25 millivolts replace the thermocouple as most standing pilot gas valves need 25 or more millivolts to keep the pilot flame lit.
If you test the thermocouple with the multimeter and you get a reading above 25 then you have another issue. Always make sure the tip of the thermocouple is directly in the pilot flame. If the tip is in the flame, you have held the nob on the gas valve down for longer than a minute, the pilot flame is strong and steady, and the pilot still does not stay lit then you likely have problem with the gas valve. Gas valves can not be repaired as per the manufacturer and need to be replaced. Good luck!