Is the tank leaking or weeping? Is the make of your HW tank an Atwood? If it is, the tank needs to have an air cushion in the tank to stop weeping. It is a good thing to try first before buying a valve.
It may be that the valve just needs to be replaced.....or it may be that the valve needs to be reseated.....pop it a couple of times, to see if it stops.
The tank really shouldn't be filled to that point anyway. You may have too much water in there. Usually, that valve is shut, when you are filling the system, and there will be a "air" space in the tank to reduce the chances of water hammers and act as a pressure tank for your system.
You may want to drain the tank (with valve open) then close the valve, and turn on the pump to re-charge the water heater....then turn it back on, and see what happens.
I'd try that before going and getting another valve....unless the valve has some age on it??
Bill & Claudia / DD Jenn / DS Chris / GS MJ Dogs: Sophie, Abby, Brandy, Kahlie, Annie, Maggie, Tugger & Beau RIP: Cookie, Foxy & Gidget @ Rainbow Bridge.
2000 Winnebago "Minnie" 31C, Ford V-10
Purchased April 2008 FMCA# F407293 The Pets
Same thing happened to me. I am staying in LV, Nevada and the water is very hard. It started to drip just a little, but then it was really coming out. I took off the relief valve to replace it, and found out it was very filly with junk and wouldn't close anymore. Get a new one.
Common problem with the relief valves. Doesn't cost that much, replace it and solve the problem. Best to get replacement at RV supply, as the ones for home use are different, usually longer. Check Camping world, give them heater brand and model, if you aren't close they will ship.
Noel and Betty Johnson 2005 GulfStream Ultra Supreme, 1 wife, 1 Poodle