Pilot light will not stay lit on model 465FX-R wall mounted gas furnace. Thermocouple was replaced but still won't stay lit. Gas is on at the meter. Any suggestions?

There are a few potential issues that could cause a gas furnace to light but not stay lit when the control knob is released. Here are a few things you can try to troubleshoot the problem:

1. Check the gas valve to make sure it is open and functioning properly.
2. Check the gas pressure to the furnace. If the gas pressure is too low, it can cause the furnace to go out when the control knob is released.
3. Check the thermocouple for proper installation and alignment. The thermocouple should be seated securely in the pilot assembly and should be properly aligned with the pilot flame.
4. Check the pilot assembly for any debris or obstruction that may be causing the problem. Clean the assembly as needed to remove any debris.
5. Check the control valve for proper operation. If the control valve is not functioning properly, it may not be able to supply the necessary gas to keep the furnace lit.

You can test the t couple with a millivolts meter it should be 17 mv minimum. If that's good and wont stay lit then the gas valve is bad. I'm assuming you are getting gas at the pilot. If not then pilot orfice may be plugged. If you get the pilot to lite and goes out when you release the pilot button then replace gas valve.also be sure the pilot flame engulfs the t couple tip or it will not produce the voltage needed to hold the pilot valve open

You may have a bad thermocouple. This is a device that when it gets hot (usually from the pilot light) enough it sends a signal (allows conductivity) which allows the heater to stay lit when switched into the 'heat' or functional mode.
It's a common safety element in all gas furnaces and stoves to ensure that the pilot says lit and no gas can escape in case it somehow extinguishes.

Pretty much the only thing that will do that is the thermocouple not generating enough voltage for the valve to say it's OK.
Usually you need to hold the button for pilot lighting for 60 seconds. You can use a meter to check that it's generating enough power. The thermocouple has to be in the pilot flame properly.

Check this video:
https://www.youtube.com/watch?v=suen7QlJl4o

Gas furnace will not light Thermocouple test with the multimeter

Or see this site:
How to Test Thermocouple with Multi Meter Heating and Cooling

It sounds like there may be an issue with the gas valve or the thermocouple on your Williams gas wall heater model # 5009622. The fact that the pilot light will not stay lit and the burners came on and went off after cleaning the thermocouple, suggests that there may be a problem with the gas valve or thermocouple. Additionally, the fact that the pilot light went off in the middle of the night, it could also be a sign of a problem with the thermocouple.
Possible causes for this issue include a malfunctioning thermocouple, a faulty gas valve, or a problem with the voltage to the gas valve.
Here are some steps you can try to fix the problem:

1. Check the thermocouple: Make sure that the thermocouple is properly installed and that the wire connections are secure. Also, make sure that the thermocouple is clean and not corroded.
2. Check the gas valve: Make sure that the gas valve is functioning properly and that it is sending gas to the pilot light.
3. Check the voltage: Make sure that the voltage to the gas valve is correct and that the wiring connections are secure.
4. Check for leaks: Make sure that there are no leaks in the gas line.
5. If the problem persists, it's best to contact a professional HVAC technician or the manufacturer for further assistance.

It's important to note that working with gas appliances can be dangerous, if you're not comfortable working with gas appliances, it's best to get it serviced by a professional.

The pilot assembly may need cleaned out and the orifice cleaned, also the gas valve may need to be replaced, to check for proper voltage from the thermocouple you need a flame source and it takes a meter that can register DC milliamps, and should be 350 to 750 millivolts. Heat the thermocouple with the pilot or other flame source and check, if OK, gas valve is weak.

I would remove pilot light assembly and clean orifice and blow out gas line to pilot. Check to see that thermocouple is centered in pilot flame. It is possiblethat your gas valve is bad but it is also possible that you got a defective thermocouple. I would change the thermocouple again as they are much less expensive then the gas valves. The next time when you are sure you have the thernocouple mounted as close to the center of the pilot flame hold the pilot button down for several mins. If none of this works then you may have to change your gas valve.Thank you.

Hi,
The thermocouple is bad and needs to be replaced...
The thermocouple is the copper rod that sticks up into the pilot flame and then screws into the gas valve...
they are sold by lentgh so you need to measure the old one when you go to buy a replacement...

heatman101

check for power from low volt side of transformer and at gas valve also check fan on other than auto.

Trane unit ,same White -Rogers gas valve. I have replaced both the gas valve and the thermocouple . Have agreat robust blue pilot while the button is pushed in , let go and the flame does not stay lit . I checked the milly D C volts and have better than 20 . Is there a problem with the new gas valve or the couple not generating enough volts or is there a safty I do not know about that could be open ?