I have a 6yr old bradford white hot water heater serial#AF4817960 and model#MI40T6FBN4. One day the pilot ight went out and when I tried to re-light it after following the procedure on the side of the tank it just will not stay lit, it do not stay lit for a moment it just won't light. Help me please somebody

You probably need to replace the thermocouple which runs alongside the pilot. It is a copper looking wire that goes from the gas control valve to next to the pilot. A 24" one should be plenty long; but be careful not to bend and kink the line. You can gently make a loop with it. Should cost less than $12.00, available everywhere.

I agree with Scott you need a new thermocouple, to replace it open the link below and watch the you tube, before you start replacing the thermocouple close the gas valve, good luck.

John

No Hot Water - How to Replace a Thermocouple - YouTube

Hi everyone!

Hey guys, I'm afraid that changing a thermocouple isn't as easy as it used to be. Here, since they started manufacturing water heaters with CLOSED COMBUSTION CHAMBERS, an individual needs to shut off the gas supply to the heater and then loosen/disconnect the gas tube, the pilot tube, the piezo ignitor, and the thermocouple from the gas valve itself and then the screws to the combustion system door and remove all of that as one piece to replace a thermocouple... see image below.

After that, the person can change the thermcouple out (may or may not need a new combustion door gasket) and then reinstall the combustion system, reconnect everything, turn gas supply on and test for leaks (leak detector/soap solution at all joints disturbed) after firing the system up.

That's how it's done nowadays guys! UGH!

Mark

John, please clarify. You say it won't stay lit, but you also say it won't light at all. Very important info we need to direct you in the right direction. If it lights but goes out when you let off the pilot knob, then I agree it may be a thermocouple issue, or it may be a limit issue (yes, some new water heater have a resetable overtemp limit, and yes, UGH! ). However, if you can't get the pilot to light at all, you may be looking at a plugged pilot orifice, lack of gas, or bad gas valve, or simply a lack of spark from the piezo to ignite the pilot, etc.. As Mark said, the modern water heaters are a bit more involved than the old standard ones. Believe it or not, some makes even require a special thermocouple assembly and are not to be replaced with a universal theromocouple.