Possible slab leak?

I recently purchased a home that was built in 65 with the original cast iron plumbing below the slab. Before I moved in I had all the plumbing replaced. Fast forward 3 months later I walk around to see two wet spots about 4 feet apart on the slab and a puddle under my dish washer on the other side of the same wall.

My fist thought was slab leak, (so with freezing temperatures that night) I turned off the water to the house drained the lines, and waited for the plumber in the morning. Next morning, with the water back on, no leak, no leak by the outdoor faucet, no leak in the wall behind the siding, no wet spot on the foundation, nothing. The plumber even did a basic pressure test on the water line. Nothing.

I kept a close eye on everything and no more problems for a few months. Water bill looks fine, gas bill isn't higher than normal, but tonight I noticed hot spots in the tile along the hot water line.

Is it possible that the hot water line is just heating up my floors through the slab?? Does it mean I definitely have a leak? I also checked the water meter and it didn't show any movement.

Any other tips or advice would be great so I don't make the plumber come back out here for nothing again! Thanks!

 

Shut off the hot water only. See what happens. BTW, how did they replace the pipes in the slab?

 

Unless you had your concrete floor cut open the pipes underneath were not replaced. So, you are still likely dealing with 50+ year old pipes. A leak under or in the slab is a very real possibility.

One step is for you to get the pressure gauge and fittings needed to perform the pressure test yourself. Pressurize the system and see if it holds for half an hour or an hour. You could hire a plumber again to do the test but the cost of the gauge and fittings will probably be half the cost of a service visit plus you'll have the gauge for future testing.

Even if you do not find a leak I would start planning and budgeting to have the water lines under your slab replaced. Even if they are not leaking now it is only a matter of time. Copper and steel corrode and it's a well known problem and a big issue with metallic piping in/under concrete slabs. You'll basically have two options. One is to really tear up your house by cutting open the concrete floors/slab to install new piping following the old routing. Or, depending on your location and house layout it may be easier and cheaper to reroute the lines to run through your attic.

 

The cast iron pipes were removed by digging a tunnel under the slab. They were replaced with PVC. The only concrete that was cut up during the process was an access hole in the garage to get to the tunnel.

Does this still mean I have more water lines to replace Dane?
I'm still not sure why I would feel hot spots, but not show increased cost in water bill or any movement on the meter?

Thanks again.

 

Hopefully all your under slab pipes were replaced though it does not rule out the possibility of a leak in the new pipes. PVC/CPVC can crack and break.

I would pressure check your water system. It's the most reliable way to determine if you have a leak. If you are on city water you can make sure nothing is running inside the house and note the reading on your meter before you go to work. Then check the meter again when you get home. Over that long a period even a slow leak should be registered.

As for hot spots I never like to rely on "feeling" but it is possible you are feeling a warm spot. See if you can borrow or rent a thermal (FLIR) camera. Looking at your floors with the camera will give you unbiased results as to hot or cold spots. You may be getting some heating of the slab from a hot water pipe especially if it's feeding something that is using a lot of hot water like the washing machine on laundry day.

 

Ok thanks! That answers my question.

I had just taken a hot shower and was doing laundry also. There were definitely hot / cold spots along the line but I wasn't sure if it meant there was a leak or was just normal radiating heat. I'll still check for a leak as suggested.