The ancient shut-off valve--hot water side--is crusty, leaking, and needs to be changed. It has 1/2" FPT and attaches to 1/2" copper which comes up through the slab. Valve is about 3 feet above the floor.

The hot water heater is about 10 feet away. It occurred to me that even with no pressure IN to the heater, gravity will force water out of the copper line, when the valve is removed, until the water height in the heater is the same as the height of the copper line--won't it?

If that's true, I guess I need to empty the water heater to below the level of the valve I'm replacing?

Thanks!

Why change it? Maybe a new washer will fix it for the next 15 years of use.

1. The water will NOT come out if you do not open any other hot water valves after you turn the water off to the heater
2. Even if water came out, unless you are the slowest person in the world, the amount of water would be insignificant.

I want to change it because it's the old style (gate?) valve, which seem to have more problems with our hard water, than ball valves. I could probably repack it etc., just prefer the simplicity of 1/4 turn ball valve.

I wondered if flow might be minimal with all faucets closed, but didn't want to chance it without asking. My experience tells me there's likely to be 'some' seepage. There is enough corrosion that I need to plan for the possibility I'll need to sweat on a new FPT fitting. I'm not the slowest around, and I do ok sweating dry copper, but if this has (who knows how much) seepage that would make me sweat!

Thanks for the advice!

Like hj said if you don't close the cold side inlet into the water heater, and shut off all hot faucets the water would be kept in place. What could happen sometimes is you turn on a single handle mixer somewhere for a second and that let air in and breaks that closed system.

If you are worried you can turn the breakers off to the heater, turn the hot side washing machine valve on plus another hot faucet and let it run into a bucket until it stops into an equilibrium. Then do your thing with a wet dry shop vac on standby. If water starts coming up you can remove that with the shop vac and dry solder then.

Why would you have to sweat on a new fitting, since you stated that the existing one is already a threaded connection?

Did you really mean to say "if you don't close the cold side inlet into the water heater, and shut off all hot faucets the water would be kept in place."? I know you know the cold water feed must be closed.

I like your idea about draining much of the heater, but since all faucets, and the washer, are higher than the shut-off valve I'd still be left with a good deal of water in the heater that's still too high--I think. But it would save taking all those gallons out the bottom of the heater I guess.

I HOPE I don't need to replace the threaded fitting on the copper line. Just planning for worst case scenario.

Thanks again.

you shut off the water, put a washing machine hose on the valve you want to replace, stick the hose in a bucket on the floor , open the valve and let whatever water that wants to come out, come out.
then you can do as you wish without worry of niagra falls..
if you do need to solder to that pipe, make a cut where you want and use a shop vac to remove as much water as you can.

yes steve I typed the opposite of what I was thinking...

Did as suggested and had very little drip from open copper lines. So much corrosion was UNABLE to unscrew hoses from valves but valves unscrewed from copper fittings without too much trouble.

These hoses had short metal L shaped tubing between hose and the 'nut'. Tubing actually broke off from nut with just gentle jostling! Guess it was considerably past time to change them.

Thanks again for the help!



Edited 1 times.

this is not uncommon. it won't happen with brass ended hoses.