During an early spring RV trip the hotwater pressure relief valve would not stop leaking. I flipped the control lever open and let it snap shut several times, but the leak continued. I forced air into the tank by turning off the water connection, opening the relief valve then opening the hotwater faucet at the kitchen sink. This allowed air into the tank. After closing all valves I tested it again with water pressure. It still leaks.
You will want to be sure the water source is turned off and the power or gas to the heater is also off. Enough "fiddling around" with the valve, it needed to be replaced. I started by removing the baffle so I could get some leverage room on the valve. Only six philips head screws and the baffle was removed.
Since the valve was still difficult to reach, I used two adjustable wrenches to begin the valve release. Be prepared for water to begin pouring out of the valve hole once the valve is removed.
Removal was easy.
I decided it was time to remove the drain plug to remove any particles which might be floating in the tank. The drain plug had an anode rod attached and was covered with hard-water deposits. After draining the water from the tank I used a garden hose to agitate the sediment in the tank and drain as much of the deposits that would break loose and exit the plug hole. I cleaned the anode rod and replaced the plug after wrapping the threads with plumbers tape.
A new pressure relief valve is not expensive and easy to install. This one came with plumbers teflon tape already installed. Waterheaters and parts can be ordered from CampingWorld.com and if you are a Presidential member, they give a 10% discount.