Main burner for hot water tank does not shut off.

Turn the gas valve/thermostat down to pilot or vacation setting... what happens then?

Burner goes out

OK...

When you turn the gas valve/thermostat back up to the correct temperature and the gas valve fires... try backing it down a little... does it shut off then, too?

Did as you ask, the burner fired up and is running

I'll repost...

I wanted you to turn the gas valve/thermostat back up to the correct temperature and see if the gas valve fires... you did that. Then, try turning the gas valve/thermostat dial back off a little until it shuts off again. Let me know if it shuts off again.

OK, turn the control valve to low. Burner is off. Turn the control valve to hot, half way between low and hot, burner is on

OK... sounds like the gas valve is in control of things. What makes you think it isn't shutting off the burner?

With no one running the hot water, burner was on for 20 minutes. Or so.

Massplumber I don't want to butt in but I am wondering if he might have a hot water leak and the heater is not keeping up with the hot water getting out of the water heater.

Not too far fetched if someone had used the water for awhile prior to this firing off like that...

Otherwise, it sounds like the gas valve/thermostat is doing its job, so I am starting to wonder if you have any pipes that go under ground? Could be a leaking pipe underground (or elsewhere... look around). Are you an a slab type house (no basement)? Are there any pipes that go underground?

Back to you...

MARK

I just posted that thought as you did letmetellyou... had to go through the steps to arrive at this... ;)

Look for a leak kmacjoe... let us know.

OK, how do I trouble shot hot water leak

Start by answering my questions...

Do any pipes go underground? Are you on a slab home (no basement)? Let me know.

Slab type.

Ahhh... this can be a bit tricky here. Sometimes you can find the leak underground by finding the hot water pipes that go underground. The leaking pipe would be hot when compared to the ones not leaking (as long as pipes remain unused). Chase out all hot water pipes that go into the floor... find the hot one.

If you can't find any pipes going into the ground it could be that they are behind the walls... gets more complicated then. Worst case, you'll need to call in a leak detector company... *UGH*!

Look for the pipes... let us know what you discover.

Massplumber- Do you mind if I as hin a question.

Nope... please do... ;)

ok, how do I trouble shot hot water leak

I have two suggestions. First is make sure that no one is using water in your house, hot or cold. Now use a long screwdriver and hold the blade end againsg a faucet in you house, put the other end against the opening of you ear, see if you hear a noise that might be water running.

Second go to your water heater and use the cut off valve that you should have at the top of the heatr. Turn the water off for a few minutes, three or four. Now open the valve back up and if you hear a rush of water that probably means that you have a leak.

OK, the hot water supply line goes into wall.
If I were to put a pressure gage on house line into the house and turn off the water line going in. watch the pressure gage for drop in pressure

Try what letmetellu suggested... if you hear water charge into the tank when you turn the water back on then the leak is confirmed... although I think issue now is to find it as we're both pretty sure you have an underground leak somewhere.

OK, I turn the water line off at the top.

OK... give it 3 minutes and then go turn it back on... if water rushes in (it shouldn't)... leak confirmed... just need to find it now!

Bad news!!
Yes I hear the rush of water going into the tank
Thanks for the help!!

Glad to help here...

For tonight I'd shut off the water into the heater and turn the gas valve/thermostat to pilot. Turn all on in the AM when needed.

Good luck... hope it's found easily!

Me to.