I've seen similar questions but didn't see the exact answer I was looking for.
I want to know what happens if I shut off the water to the house and
Go on vacation and leave the hot water heater on and then a leak in
A hot water faucet develops. Would the heater tank drain, overheat, and
Cause trouble?

Thanks,
Alan

In short yes. If you are going on vacation and wish to turn your water off I would advise
Turning the water heater off as well.

Water expands and contracts as it heats and cools. Normally this is accommodated by water flowing in and out the inlet. Shut the inlet off with unheated water in the tank, and it is going somewhere when it heats. If you are lucky, out the relief valve. Better yet is an expansion tank.

So shut the water off and leave the tank on? In the first heat cycle it may force water out the relief valve. It will then draw a vacuum unless air leaks in the relieve valve. Relief valves are notorious for leaking a little once they have opened due to lime or other crud getting on the seat.

If a faucet developed a leak, not much would happen with no pressure at the tank inlet to force water into inlet pushing it out the outlet. Try it. Shut the water off and open a hot faucet. All you should get is what is in the line.

I would kill the hot water heater too. I don't think stand by losses are what some claim, but no sense paying to heat water just sitting there while you are gone. The tank itself could develop a leak too.

Lab just gave you excellent advice. Shut the heater and water off when you leave. Turning the water off is the cheapest insurance that you can ever have. If you've ever come home to a small leak that's been running for a few weeks it could really put a downer on your vacation. Regards and have a good time. Tom

Water expands and contracts as it heats and cools. Normally this is accommodated by water flowing in and out the inlet. Shut the inlet off with unheated water in the tank, and it is going somewhere when it heats. If you are lucky, out the relief valve. Better yet is an expansion tank.

So shut the water off and leave the tank on? In the first heat cycle it may force water out the relief valve. It will then draw a vacuum unless air leaks in the relieve valve. Relief valves are notorious for leaking a little once they have opened due to lime or other crud getting on the seat.

If a faucet developed a leak, not much would happen with no pressure at the tank inlet to force water into inlet pushing it out the outlet. Try it. Shut the water off and open a hot faucet. All you should get is what is in the line.

I would kill the hot water heater too. I don't think stand by losses are what some claim, but no sense paying to heat water just sitting there while you are gone. the tank itself could develop a leak too.

Thanks for the info. But, if I shut off both the water to the house
And the water heater at the same time, the water in the water heater
Will cool off, shrink, and create a vacuum and that's not good, I assume.
Comments? By the way, I'm already on vacation (for 5 days) and
Have left the water heater on but the water to the house
Turned off -- then I started to worry and posted my question.
I have done this before without a problem
But it occurred to me that if the hot water valve to the washing
Machine failed, I could be in trouble. It once
Failed while I was on vacation and I had left
The water to the house on. Fortunately, a contractor
Was doing work in the hosue while we were away and saved the day.
I'm looking for the best way to leave the house. I don't like
Lighting pilot lights, etc, so I was hoping leaving the hot water heater on
Was going to be fine.

If the washing machine valve fails with the cold water supply cut off to the water heater you would only get a small amount of water into the washing machine if any.

In my original post I mentioned open a hot water faucet. That would allow air or water in and out. Just close it once the air is out when you come back and start turning things on.

The water heater should stay full or almost full. Leaving the pilot light on really shouldn't hurt that much.

I think you actual question was "Would the heater tank drain, overheat, and
cause trouble?" and the answer to that is no, no and no. Everyone else is correct and you should shut off your water and the fuel to the heater. It is the wise thing to do. However, you asked if the tank would drain if your faucet leaked and it will not. As soon as the pressue bleeds off the leak will stop dripping and the tank remains full, it won't overheat either and no new trouble will come of it since there is no longer pressure in the lines. Since your heater is gas just turn the knob to pilot only and you won't have to reignite the tank when you return home.