Hot water heater relief valve opens

[wooden head]

Quick search found what looks like a pretty good article on the subject. Was actually looking for a go to of an explosion as people tend to think I'm kidding. Search water heater explosion you will find some good ones including mythbusters intentional explosion.
The article below refers to an explosion in Seattle I knew a plumber involved, it was a six gallon tank.

http://stevedmarineconsulting.com/water-heater-primer/

[ValiantV]

Does the inlet to the water heater have a check valve to prevent water from flowing back out if the tank? You mention you leave the pump off, so I could see this happening.

If that were the case, I think it is possible for the water level to uncover the thermostat and cause a situation where the temperature is not properly sensed, and the element stays on linger than it should.

Do you have this problem if you leave the water pump on? Do you know if a check valve is installed at the inlet to the tank?

I tend to leave my water ump off when I'm not using it as well (still chasing leaks in my old boat) but I make it a point to pull the water heater breaker when I do this - just to guard against uncovering an element and burning it out.

[ValiantV]

Originally Posted by buzzstar

With all the previous good advice, it is now safe to ask the question, Why are you heating hot water? The thread title could explain the problem.

Channeling George Carlin?

[Uncle Bob]

Originally Posted by wooden head

Quick search found what looks like a pretty good article on the subject. Was actually looking for a go to of an explosion as people tend to think I'm kidding. Search water heater explosion you will find some good ones including mythbusters intentional explosion.
The article below refers to an explosion in Seattle I knew a plumber involved, it was a six gallon tank.

Water Heater Primer | Steve D'Antonio Marine Consulting

The article quoted refers to a heater that had the relief valve capped, as in deliberately made non functional, and was partially drained yet still connected and operating so bears no resemblance to the OP's situation which has the relief valve weeping occasionally.
Check the temp, if too hot and not able to adjust the thermostat, replace same.
If correct temp, replace relief valve, they do fail sometimes.
If you want to make the system virtually bullet proof, install a relief valve of a slightly lower pressure in the inlet line and if the pressure should rise to a dangerous level there are two sources of relief. This does work, it's how my house system is installed.

[Kentb]

Verify the temp is 140 degrees or less, and the presssure is not too high( probably less than 100 lbs).
On my residential homes I have seen a plumbers trick where he takes a hammer and softly taps on the center of the relief valve to seat it. Whatever you do, don’t cap it. I am sure someone will come on here and proclaim doom and gloom for tapping on it, but it has worked in units that accidentally had the manual trigger pulled, but then continued to leak.

[wooden head]

I know what happened with the heater in the article. It also goes on to discuss the t&p further specifically in a marine application. The warnings in my post and the article are because people routinely cap these to stop leaks.which is a baaad idea.also with no cold water incoming it negates part of the safety fuction. My fist concern is that the op knows the safety issues so no one gets killed.