My neighbor bought a new electric water heater yesterday, and started installing it himself. He's in his early 80s, so it was quite a job for him. His wife called Saturday evening to see if I'd "drift over" to see if I could help him.

I did a few solder joints, and hooked up the wiring. We did a pressure test, and had to fix a little weepy leak in a threaded joint he'd done earlier. No big deal. We switched the 30A breaker for the water heater on, hear the element come on, and the outlet pipe starts getting warm. Everything seems OK, so I go home.

This morning I learn that about an hour after I left, the 200A main breaker tripped. They switched the 30A water heater breaker off, reset the main, and left it like that for the night.

This morning, I took the covers off, and saw nothing amiss with any of the wiring. The thermostats were set at about 125-130 degrees. We switched the breaker back on, and I left. After about an hour, the safety valve pops, spraying steam out the discharge pipe. They switched the 30A breaker off, closed the supply valve, and there it sits.

I see two problems:

First, why did the 200A main open up when the circuit to the W/H is protected by a 30A breaker? They've owned the house since it was built in 1987, and there's never been a problem with the electrical system. They couldn't recall the main ever being switched off.

Second, why didn't the thermostat(s) open up before the tank overheated. I guess one or both must be defective, but I can't figure out a way to determine which one is bad without disturbing the wiring. I don't want to void the warranty by fiddling with it. So far, I've done nothing more than look around.

Any ideas on what's going on?

Obviously, they're going to call the people they bought it from, but I doubt they have a way to get it fixed without calling a plumber and/or an electrician. I'd hate for my neighbor to have to remove the defective W/H and install a replacement if they just want to give him another one from stock.

Roger