I have a 50 Gal BW Defender. Model M45036FBNS Cannot find a service manual for it anywhere that would explain how to remove the burner and pilot tube to check and clean. Periodically the heater goes out and I have to press the reset switch to get it lit. Sometimes I would have to get into the air vents with compressed air if it would not lite and that would solve the problem. Although once some dust got up into the spark arrester and it popped! Today, I have not been able to get the burner to stay lit for more than a half hour or so. I blew the screen off. At times today the burner would lite but only when the temp was on a very hot setting? Now the pilot will stay on but the burner will not lite. Is this the thermocouple, the main valve or could the tube be clogged. I have taken off half of the access door enough to gain access to the inside of the heater but have not removed the burner, or the tube to clean it. I am not sure how to get it apart. If anyone can help would this I would really appreciate it. I do just about all of my plumbing, running lines, including my main line, sweating my shut offs, prv etc, but have not had the water heater apart. It cannot be that hard, but I cannot find the specs for it. I have two half doors that crimp around the thermocouple, the ignition wire and the pilot tube. Do I take all of those off by removing the nuts and then just pull it out? Then how do I get the burner out so I can clean it? The plumbers in the area that I know do not work on heaters. They only replace them. For that matter I can do that, but I have only had this heater about five years. By the way, I found some pieces of metal rusted at the bottom of the tank. Is it possible that pieces of the flue would rust and break off?? Anyway, if anyone can help and talk me through the process of taking apart so I can check and clean it I would be appreciated. I am learning that Bradford White heaters seem to have problems. Any recommendations for more reliable heaters. Thanks.
Here's the service manual
or it could be this one
I don't think it's your thermocouple if the pilot is staying lit after you turn it to the on position. If it only worked before on the hottest setting and now its not working at all it sounds like the thermostat or something. I don't know, I don't know much about water heaters but I had a problem with my Bradford White Defender, finally just replaced the thermostat/gas valve and it's working fine. But I recommend you make sure that's what's causing the problem before going and replace it. Hope this helps. Good luck.