My house is on a slab. In the main bathroom, when you turn on the hot water in the shower, it just trickles. The cold works fine. Both the hot and cold water in the vanity work fine. So i thought the shower valve was bad and replaced it. Still no hot water. So I think I have a leak in the hot water line between this shower and the vanity or, some calcium build up clogging the line. So I stuck my air hose down into the hot pipe and blew air into it. But water came gushing out of the cold pipe. This makes no sense to me. Is it possible I blew water through this hot pipe, back to the vanity, through the vanity faucet, and back down through the cold pipe, and out the cold pipe here at the shower? I’m going to re-plumb this shower and see what I get. But does anyone have any ideas why there’s no hot water or how the air pushed water out of the other pipe?

Slab shouldn't have CPVC in the slab......... Cap it off, make sure all water faucets are off and watch the meter. If it's running you could have a leak for sure

I will try that. But just out of curiosity, why would they not use CPVC in a slab? Every thing here is CPVC. Is that bad?

I also have another question? Why would they leave this big hole under the shower? It seems like a good way for ants and termites to get into my walls. Or radon gas.

If the slab moves the pipe will crack. Not sure how old it is. Now they use pex older home should be roll copper. Drains can be PVC. That hole is for the P-trap. I'm not a plumber though. Maybe one will chime in

The house was built in 1993.

Originally intended for granite and tile shower stall.

Probably not inspected. You can put a little concrete in the bottom. That's a tub isn't it with a shower. Hole has the drain and trap in it.

CPVC shouldn’t be in the slab. It gets brittle over time.

The hole is so you can hook the drain to the trap. It looks big until you start to hook it up. Do not fill it in. If concerned about critters, spray some bug spray in the hole before you close up the wall.

The water came out the cold pipe because it fed backward through your water heater. The cold line being uncapped there gave the air a place to go. That’s the only connection where cold and hot mix. Cold goes into water heater, hot comes out.

That makes sense. I went ahead and put it all back together and now the hot water works normally. It mush have been some calcium or something clogged somewhere. I guess I will know if it happens again. Thanks for your help!

Glad you got it working again

Coolness!!

Thanks to everyone!

Any little pebble in the line will reduce flow through the valve assembly. If it starts doing it again this will likely be the culprit. Getting it out is a whole nother animal

The knobs where they open can get crap in them too causing the issue had it happen several times.