Ruud PVP75E-IP Water Heater

The thermostat shuts off the main burner.The pilot light gas is controlled by the thermocouple which the side of the pilot flame has to envelop. If the flame is too small or too far away from the flame, it shuts the gas off to the pilot. The thermocouple generates a small voltage which keeps the pilot gas open. It can over time fail itself, so look at replacing it. The thermostat sounds like it's failing too.

1) Copy following link to troubleshoot by type of gas control valve:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

2) Otherwise Rheem-Ruud does not post service manuals
http://www.ruud.com/products/tank_water_heaters/gas_water_heaters/

3) Sound like bad gas control valve thermostat.
Newer Honeywell electronic controls can be replaced without draining tank.
Older mechanical controls are replaced by removal from tank after tank is drained.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Well I you have the problem resolved by now, but I will answer anyhow. This just happened to me yesterday with the same water heater that you have. My problem was that the flame sensor was dirty and not picking up that the burner was lit, so it shuts everything down and goes into lockout mode. I had a similar problem with my furnace lighting system. It is called flame rectification. What actually happens is the flame itself allows a small current to flow through it, so the flame sensor actuall makes electrical contact with the burner. The control senses this connection and knows then, that the flame is on. If it doesn't sense this connection, it thinks the flame is out, so it must shut off the gas valve to prevent a possible explosion. Take your burner out and clean up everything in there, being careful not to break the small glass bulb inside, which is another safety device. Fine emery cloth of a wire brush will clean up the flame sensor good. Also wire brush the burner itself, since this is the other end of the rectification circuit.

the thermal coupling may be bad!! if the coupling goes bad it will shut down flame. its a safety feature, if gas comes out, and no flame it shuts gas off. the coupling is in pilot light flame and works on the same principle as a thermometer to sense the heat. good luck !!

check the thermal coupling for the pilot light. if it goes out it will shut down gas supply, its a safety feature to put out pilot light if the thermal coupling is bad. to prevent gas from leaking and causeing a fire. check coupling.

i think your flame sensor is bad but you will need to confirm that with rheem i am unsure what the c7 is for but code 12 is flame failure and there could be carbon build up on the flame rod...

there is a small dia copper pipe which has a thermal coupling on it the end of it sits in the flame of the pilot light,
if it fails which it does after about 25-15 months,it shuts down the gas burner

Sounds like the burner flame may be too strong (jumping out from burner tube) . Some people think the louder the better, but that is not correct. When burner shuts down like that, it has a tendency to snuff out pilot as well. Adjust your air shutter at burner so that the flame is a nice blue, or with just a hint of orange/yellow at the tip. Whatever setting that keeps the flame solid from burner tube, and not a big gap between tube and flame. Signs of soot (black) up the cover, or side of trailer means it's running too rich, and you've gone too far thus needs more air. Keeping the flame blue but still right out of the burner, actually heats better, is quieter, and should eliminate that pilot getting snuffed out. Pilot should also be a nice blue flame as well. There may be a problem with positioning of the burner tube as well, but doubtful if it has been running well in that position before. Let me know what happens.

The flame sensor is not sensing flame and the unit shuts off on safety. You can try cleaning the sensor, but will likely have to replace it. Also clean the burners. Sometimes there can be rust, dirt, or other dibri that causes an improper flame pattern and prevents the sensor from being fully in the flame.

With some units, the flame sensor is a seperate part, with others it is a part of the ignition assembly. Those can typically run 30 to 80 dollars for the part.

If the thermocoupler is defective the gas to everything is shut off. The coupler is the bulb that sits ib the pilot flame If it doesn't heat up it will sense no pilot and shut the gas off. They don't cost much and are easy to change. Good Luck, Ned