Pilot doesn't stay, so just replaced it with a new one. But same problem returns. The feature is:
1) no problem to light the pilot in any first try when the chamber (so tank) is cool or cold.
2) once water is heated, pilot became off. Re-lighting will not work until after a few hours when the chamber is cooled down.

Do I need a new valve? Just don't understand why the pilot depends on the water tempature. Thanks ahead!

>>>>>> Moved Thread from Electrical<<<<<<<

Every time this electrician tries to light a pilot, he singes his mustache.

The pros here will help.

Most likely there is a safety thermostat that is either preventing the tank from overheating from a faulty thermostat or it is bad and cutting out to early. Do you have a way to test the water temperature?

Xioajian...

What name brand of water heater?

How old is the water heater? This will tell us if you have an open combustion or a closed combustion chamber. Let us know, OK?

Could be a vapor switch is sensing vapors or is defective...

Could be that combustion make up air is a problem...

Will need your answers to tell you more... ;)

Mark

Thank you all for the inputs! Mark, thanks. Here is details:
1) model is Bradford White
2) just replaced the pilot thermal couple. Now the pilot can light up to 12 hours without problem.
3) If turn thermal knob to on, and rotote the thermal controller to warm/hot, the burn will start burning. After 20-25 minutes, the water get fairly hot, then the system shut down itself, both burner and pilot at the same time. Once shut down,
a) I need to wait a few hours, seem wait the tank water to get cool off
b) seems to need turn the thermal controller to off and warm a couple times, during turning, I can heat a switch clicked once when turning to cooler side, and once when turning to hot side.
c) then I can light the pilot and things repeat from step 1.

I feel it is like there is a thermal sensor in the water, which shuts off the system when water gets fairly hot. But the manual book ndoesn't mentioin about the part. May be this sensor is integrated with the thermal control unit. If so, the malfunctioning of this part may force me to replace the control unit, or replace whole tank since the cost is probably similar. Please advise.

Finally, the tank is 10 years old. I have never inspected/changed anode. Is this related? Also where is the anode, unless screw off the top cover, I don't see it anywhere. But openning the top cover is not easy. Also, I didn't do "montly drain off a gallon of water to remove silt and sediment", can this cause this problem? Thanks for avdance.

The anode rod cannot cause this.. entirely different purpose... read up on anode rods online at this site... neat stuff!

Here, I suspect a combustion air make up issue... maybe. However, each unit is so specific in make up air/combustion chambers and just last month I found an AOSMITH water heater with an actual WATCH BATTERY in line of the thermocouple pathway that I have decided to advise a quick call to each specific manufacturer. In the end, these guys are experts in their product and will fix this if possible with a 10 Y.O. heater.

To start, check out the troubleshooting guide at:

Bradford White | Troubleshooting -- Gas

If this troubleshooting lisy doesn't help and if you have trouble finding a local guy let me know and I'll connect you with my local guy, OK?

Mark