Tub/shower valve replacement, Galvanized to PEX?

[sowsear]

I have a 1950's home built on slab with galvanized plumbing that is mostly still functioning. I am midway into a bathroom remodel that includes replacing the tile in the tub/shower. The tile was damaged all the way thru the wall so this had to be done to make the house habitable.

I want to replace the tub/shower valve. The first plumber I tried told me that replacing the valve could not be done without risking a catastrophic failure. We then proceeded on the project trying to make it work with the existing valve which now looks like a mistake.

At some point in the past, a prior owner re-plumbed all the hot water lines with copper tubing from the water heater to all the hot water outlets/valves through the attic. The cold remains intact and running thru the original galvanized to all the outlets/valves.

We have now gotten to partial completion of the job with a lousy tile patch fix attempting to use the old valve and retro fit parts of the old trim. It doesn't look like it will work and I am considering going back to ground zero and starting over.

Is it advisable cut the galvanized cold water line and use a compression fitting that converts the water line to PEX in order to have good connections to install a new valve? Another thought is to run PEX thru the attic from the main line at the inlet to the water heater to this valve and leave all the other plumbing intact, cut the galvanized cold in and stub it off with a compression fitting. Is there another way get cold water to the valve without redoing the plumbing in the entire house?

This house is destine for a complete remodel but that cannot happen for 3-5 years so I am crossing my fingers and hope I can get that much time out of this fix.

 

[Terry]

You can't compression connect to galvanized. You could do that off the 1/2" copper, or just solder using the copper to the new valve. I prefer soldering.
You will want to raise the valve higher, and make sure you use either copper or pipe nipples for the tub spout.
No PEX can be used on a tub spout anywhere.

On the cold, if you touch that, often the copper threaded onto galvanized will start eating away the steel. Sometimes I have to cut and rethread the pipe. If you can run new line, now is the time.

 

[Sponsor]

 

[Jadnashua]

Galvanized through, in, under a slab is a ticking time bomb. It's not a question of if, but when, it will start leaking (not that it might already be doing it! You'd probably notice if it were the hot line, and they did and replaced it, but it could still be leaking on the cold, and you may not notice.).

As a test, make sure nothing is using water in the house, then write down where the water meter readout is...let things sit for at least an hour or so (overnight is better if you can remember to not flush a toilet or something!), and then see where the meter readout is the next morning...it should not have moved. If it did, you have a leak somewhere. Now it could be a leaky faucet, but if you've resolved all of those, then it's more likely a leak under the slab. Any areas around the house that are perpetually wet? Grass greener in some areas than others?

FWIW, your tub spout needs to end up with an air gap above the rim of the tub...yours might be close, which is why moving it up was suggested. That can be an issue, depending on the trim unless the whole valve were moved up as well. During a normal remodel like this, the plumbing inspector would likely ding you for not updating the valve to one meeting current requirements for anti-scald technology. That could get ugly later on after the walls and tile were up!

Doing anything to galvanized now might open a can of worms. It would be good to budget for repiping in your future, and abandoning what you have in the wall for this remodel if you can find the other end and cap it so you could only have to do part of it. You'd have to be careful about running any pipe in the attic, as it could get extremely hot or freeze, depending on where you can run it relative to the insulation and where you live. The good thing about pex is it is not damaged by being frozen, but it will, or at least can, damage fittings.