Re: OT hot water heater

Posted by docmirror on November 02, 2016 at 13:18:55 from (107.213.165.255):

In Reply to: OT hot water heater posted by ericlb on November 02, 2016 at 08:58:37:

First, I'm not a pro plumber. I do have a number of rentals which I maintain, and I've come up against this one before. Not a fan of throwing parts at stuff, but it sounds like you've diagnosed it fairly well if there's no thermo circulation going on in your plumbing from hot to cold side. You can also test this by turninf off the inlet from the cold side to the water heater and letting it sit for a few hours. These situations are common where you find a lot of single handle faucets where the water is mixed in the ball at the base handle. They can leak around.

Anyway, that silver thing is the gas control thermostat.

https://hdsupplysolutions.com/shop/p/rheem%C2%AE-propane-gas-water-heater-valve-p737841?gclid=CL6QrersitACFQuSaQodkxcLwg

The brass looking thing sticking out goes into the tank, and the whole assembly screws in with pipe threads on the back of the valve. The brass thing contains a temp sensor which will open and close the gas valve based on expansion of the fluid/gas inside the tube. There are fittings for the LP inlet line, and two or three terminal connections for the pilot thermocouple. Of course, it may be one of those pilotless types, in which case, you're beyond the scope of this discussion. Assuming it's not the pilotless type, there's a thermocouple down in the lower burner area which keeps the gas valve ready for operation, and provides the pilot for the burner to turn on when the gas valve is opened.

The sensing of the water temp is done inside that brass tube, and they do go bad sometimes. The temp setpoint dial adjusts the pin that operates against the expansion gate pin inside the brass tube to regulate the on and off of the heater. Since you've had no luck changing the temp setpoint, it possible that metering pin in the brass tube has gone haywire.

It's not a hard job to replace. Turn off the water pressure in the cold delivery side to the heater. Drain the tank below the level of the gas valve. Turn off the LP supply to the valve. Undo the LP fitting to the valve, and the fitting that goes down to the burner tray and disconnect the wires from the thermocouple. Now, the whole assembly will unscrew from the water heater, but you typically need a massive wrench on the body, or sometimes there is a square or six flat behind the valve body where you can get a large open end wrench in. I've also put a stub of pipe on the inlet, and use the stub as a 'wrench' to turn the whole valve. Remove the old valve, use some thread seal, and screw in the new valve, connect the thermocouple, LP lines, turn on the LP supply and check for leaks with soapy water around the LP inlet and outlet. Fill with water, check for leaks. Follow the manual to start the pilot, and turn it on. Once the pilot will stay on, turn on the gas supply on the valve and wait for the gas to kick on to the burner. Check again for LP leaks on the outlet side of the gas valve. Let it come up to temp, and then take a shower. See if it cycles like before, or if it's too fast again. If too fast cycle, you have a water circulation problem.

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