Pilot won't stay on.
I replaced thermocouple.
NOw the pilot stays on, burner turns on, tank heats up, pilot goes out, relight tank same problem, pilot goes out after tank heats up. Can the problem be the thermostat valve?
The problem will be either the pilot is being blown out by the main burner (not very likely) or that the snap disc is tripping.
What is a snap disc?
It can be found just to the side of the burner pipe on the outer casing with 2 wires attached. It is usually about the size of a penny and is round with 2 screws holding it onto the casing.
The snap disc is a safety device that will shut down the water heater if the temp on it's surface gets too high. This is usually caused by the flame rolling out the front instead of upwards. This is why for this application it is often called a flame roll out sensor.
What causes it to trip is usually that the vent isn't drafting properly and the flame is searching for combustion air.
To test for this light the heater and hold a smoking (not burning match) beside the draft hood (the funnel that connects to the tin vent on top of the heater). It the water heater is drafting properly you should see the smoke being sucked into the vent. You may also have a problem with not enough combustion air in the room. How is air getting into the room? is the room sealed too well? that can cause the flames to search for air. Try leaving the door to the room open to test this.
One other problem could be that the part is faulty. Try using a jumper wire across these points to eliminate the snap disc to see if the water heater will run. But remember this is a safety device and shouldn't be bypast for anything other than testing.
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Suspect the thermocouple that senses that the pilot is lit. This device prevents the gas burner from coming on when if the pilot goes out, but if it's defective could cause the burner to shut down even when there is a pilot flame. Also check the position of the thermocouple in relation to the pilot flame. The tip of the thermocouple should be right in the middle pilot flame.
With FVIR protection: Get more fresh air to the unit. Clean the flame arrestor screen. Test and replace the thermocouple: http://waterheatertimer.org/How-to-test-water-heater-thermocouple.html Inspect and clean burner and combustion parts Test gas pressure, bleed air out of gas line. Replace gas control valve. Test draft air by lighting match and see if smoke is pulled into the vent pipe at draft hood on top of tank.
Make sure thermocouple tip is seated inside the burner flame. Make sure thermocouple is not overtightened. Finger-tight + 1/4 turn. If the pilot lights, then ECO energy cut off is not tripped, but gas control valve might be bad. Check color of pilot flame: it should be strong and clear blue. If pilot flame is weak, or color of flame is yellow-orange: Clean pilot orifice and burner and combustion parts on yearly basis. Clean air intake screen if applicable. Increase air supply to water heater. Open a window and see what happens. Check for adequate draft going up chimney using match under vent hood to see if smoke drafts immediately upwards. Bleed air out of gas line. Check gas pressure.
Hopefully just the thermocouple. The thermocouple is the small rod right next to the pilot light. The flame on the pilot heats up the thermocouple and keeps the gas valve on. You can replace it yourself. The thermocouple will be connect by a small nut on the underneath side of the valve, and you will have to pull the thermocouple out of the pilot assembly. Not an expensive part, you can get it at any hardware store. Hope this helps you .
What you describe is typically caused by a faulty thermocouple. The thermocouple senses the heat from the pilot light and TURNS OFF the pilot when it no longer senses the heat. When the thermocouple turns off the pilot, it's not necessarily dangerous, but the water heater won't turn on without help.
The pilot light on hot water heaters is controlled by a thermocouple, a small copper rod that usually sits in or very close to the pilot light flame.
When they go bad, which is not unusual, they do not allow the gas line to stay open and feed the pilot light.
The easiest thing for you to do would be to replace the thermocouple.
When following the pilot light lighting instructions, be sure to hold the valve button down for 30-45 seconds in order for the pilot light to heat the thermocouple prior to turning on the gas burner.
Possible thermocouple is defective. The thermocouple is heated by the pilot itself, the theory behind this safety design is so the main burner cannot come on, if the thermocouple won't stay hot, it reduces the chance for a huge gas buildup in the burner compartment and possible explosion.
I have also seen cases a pilot would not stay lit if the flue for the heater is blocked by a spider web, bird nest or other obstruction.
Check and make sure the flue/vent is absolutely clean and clear, if it is, then the thermocouple may be defective. If you have an electric pigtail on the thermocouple, the problem may be the electronics or circuit board.
The pilot assembly should look similar to the pic above. Depending on where you live, you may be required to hire a certified plumber to replace the parts. If not you can do it your self. Keep in mind if it's not staying lit you also need to check the thermostat and the thermocoupler before replacing the pilot assembly. There is a good chance it is just the thermocoupler going out. It is one of the first things to check when troubleshooting a pilot light problem with a gas water heater. A thermocouple determines if the pilot light is lit. If it's not lit, the gas valve fails. If that's the problem, replace the thermocouple.
Shut off the gas valve on the water heater and the gas valve on the line near the heater. Remove outer and inner doors, and loosen the pilot and supply tubes and the thermocouple connections to remove the burner assembly.
Loosen the screw holding the thermocouple to the bracket. Remove old thermocouple. Bring it with you to the store to ensure you are buying the proper replacement.
Install the new thermocouple. Position the thermocouple so that the pilot flame heats 1/2 inch of the tip.
Reinstall burner assembly in the water heater. Tighten burner supply tube, pilot tube and thermocouple connections. Tighten thermocouple no more than a quarter turn more than hand-tight.
Turn on both gas valves. Check supply tube and pilot tube for leaks with soapy water. If soap bubbles, tighten connections to fix leak. Ignite the pilot light, and make sure the thermocouple tip is heating up. Replace inner and outer doors.
If possible, remove the pilot gas assembly and clean the gas jet and thermocouple - they can get carboned up and stop working properly. Make sure the pilot flame and deflector is aimed properly and making the thermocouple glow red hot. If the problem persists, you may want to replace the thermocouple and also check the propane regulator.