I’m trying to understand a plumbing leak in my house before we call a plumber. Our water heater is in the garage and about 20 feet away it there’s a copper pipe setup that looks like an “M” shape where several copper pipes branch off and then go straight down into the concrete slab. From what I can tell this seems to be where the hot water splits off to different parts of the house.

The leak only happens when the hot water line is pressurized. If we close the hot water valve at the water heater, the leak completely stops. As soon as we open that valve again, water starts leaking even if no fixtures in the house are being used. My dad says the water is coming out right at the base of one of the copper pipes where it enters the slab, not somewhere along the wall or floor seam.

Because of that I’m trying to understand how the piping is probably laid out. My assumption is that hot water leaves the heater, goes through that copper header, and then those branch pipes go into the slab and run to the fixtures like bathrooms, kitchen, etc. I’m wondering if the leak is likely right where that pipe enters the concrete or if it could still be somewhere farther down the pipe under the slab and the water is just traveling back along the pipe path.

If a plumber came out and determined the leak was on that branch line going into the slab, would the normal fix be to cut and cap that copper pipe above the slab and then reroute a new PEX line from the hot supply to the fixture instead of trying to repair the pipe under the slab? I’m mainly just trying to understand if this situation usually ends up being a slab repair or more of a reroute situation.

Hot water leak coming from copper pipe where it enters slab near heater