Gas wall heater

Thermocouple sits in the pilot light flame and generates a small amount of electricity that tells the control that the pilot light is lit. If the pilot goes out, it shuts off gas so the place won't fill with gas and explode.
https://www.youtube.com/watch?v=igxYxhD82lU
Thermocouple What is Thermocouple How does Thermocouple work

http://en.wikipedia.org/wiki/Thermocouple
Thermocouple Wikipedia the free encyclopedia

Thermostat flame sensor. Do you see a little rod next to the pilot? That is what tells the main gas valve that the pilot is lit and it is safe to give gas. Easy swap, and you can usually just pick up a generic one.

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.

1) Get more air to the water heater and see if problem continues.
2) Read the following pdf-s for things that might apply to your situation.
http://waterheatertimer.org/images/Negative-pressure.jpg
http://waterheatertimer.org/pdf/Attic-Ventilation-and-Pilot-Outage-in-Gas%20Water-Heaters.pdf
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf

3) Read pdfs above first, and then Add a comment with missing information below, for possible do-it-yourself help.
Does this water heater have a blower?
Is gas valve electronic? Or does gas valve have a dial?
If gas valve is electronic, have you checked outlet with circuit analyzer?
Did pilot light work correctly for a while? If so how long?
Where is water heater located? Hot attic? Closet? Garage? Is area dirty and dusty? Has air intake been cleaned?
What color is pilot flame? Clear blue or yellow-or-orange?
Have you inspected inside of combustion chamber for dripping water?

SEt to pilot, Push knob, push pezio ignighter until pilot lights, hold for 30 seconds. if it stays lit turn to on, if it doesn't stay lit, you have a bad thermocouple

Dust has built up in the ODS pilot safety. Blow out the pilot or flush it with Rust Buster. Let it dry and retry.
How it works/What to clean HERE

If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

There should be a thermocouple in front of the burners that has a copper colored wire that runs from the gas valve to the thermocouple. It is located in the pilot flame as it is a pilot proving switch that tells the gas valve the pilot is lit and its okay to open the gas valve to the main burner.

how by extending the duct work will it make the gas valve work ?

if the pilotkeeps going out clean pilot jet , or if the power unit has gone in the gas valve then you would have to change the valve , don't get the flue bit ?

you most likely have to replance the thermocouple, its a safly feature that tells the gas valve that there is a flame present, if its not working its telling the gas valve that the pilot is not on and not to turn on the gas. If you look at your pilot light its a small metal rod that sticks into the flame, it should trace back and go directly into the gas valve.

A short pilot flame not playing on the thermocouple or a faulty thermocouple , loose connection at the gas where thermocouple is ,

blocked pilot flame to small , air in gas line did he purge the gas line first? other wise you will be there a long time .