Need advice.

Noticed a warm spot in the tile of the front bathroom yesterday afternoon but didn't think much of it. It was there still this morning so started to think the hot water line is leaking in the slab.

San Antonio (78209) house was built in early sixties and I know there has been at least one hot water line in slab that has been capped and re-run through the attic. Diagram below shows where the hot spot and lines are. The hot spot is about 75 degrees vs 70 in the surrounding tile when checked with laser temp gun.

I shut off the toilets (one runs just a tiny bit) the sprinkler system and fridge ice maker and took pictures of the outside meter over time. The main gauge for cubic feet didn't move over the course of 8 minute span, then 30 minute span. However, the little spinner to show leaks moved about an 8th to quarter of a turn in 30 minutes. Movement not visible when staring at if for 5 minutes.

I then bought a pressure tester and hooked it up to hose bib out front and shut off water to house.
62 PSI at 1:22
60 PSI at 1:36
56 PSI at 1:50
56 PSI at 2:20 (seems to be holding)



There is an open space through a cabinet in master to get under the front bath tub water pipes. There is no leak there and nothing coming in from the warm area. The pipes under the front sink all seem fine, no leaking right there at least. See blue checks in picture above.

I assume this is all pointing to a leak in the slab line between front sink and master. Anything else to test?


Alternatives for fixing? Here is what I got, what am I not thinking of?

1. Dig up leak and fix pipe.
- Seems like an expensive disaster that will lead to remodel of front bath but not master bath. Will eventually need to re-do the whole house down the road as this will likely happen to another line down the road.

2. Re-pipe whole house (hot and cold) through attic.
- Re-pipe and run Pex for hot and cold through attic to the different hot water faucets (kitchen, front bath & sink, master shower & sink)
- also expensive but at least modernizes
- Gets into remodel territory as well but we were planning on doing that at some point for both bathrooms anyway
- Kitchen - We ran PEX to kitchen to future proof when we remodeled it in 2020, just needs to be hooked up (DIY?)
- Front bath - Can get to front bathtub faucets and drain through cabinet with minimal destruction and need to remodel tub and enclosure. Getting Pex to sink would require some demo and remodel but again we were planning on doing this at some point. So just a partial remodel for front bath.
- Master bath - would have to demo shower enclosure to get to faucets, same for master sink, so that basically kicks off full remodel.

3. Re-pipe hot water only from guest bath to the other hot outlets through the attic.
- Less piping (no cold) but still requires destruction in some walls to replumb everything.

4. Same as #2 but go extra step of replacing 12+ year old tank water heater (in garage) with gas tankless either in same location or on exterior of house and setup PEX manifold for new pex lines to be able to shut things off more easily.

Any ideas for simpler, less expensive solution?


In the meantime, what risk is there if we run the hot water periodically when needed for shower/baths, dishwasher (could do by hand) but shut off main hot water valve in between?
Should I keep water heater on while water is turned off? Seems like risk of burning up if water evaporates or someone opens a valve and drains hot line.


I can get more pictures if it helps.

Re-checked all valves in house and one toilet was not closed all the way. PSI started at about 63 and now at 60 after about 35 minutes. Not sure if that is normal. Maybe it will hold.

Assuming the bathroom is on an exterior wall go outside and see if there is any staining on the slab (or if it's wet).

You can also shut off the inlet at the water heater, disconnect the outlet line and pressure test it if you have a compressor and rig up a gauge with a valve and air nipple.

Unfortunately it's in the middle of the slab, not near exterior wall.

I have a compressor and might be able to run an air test.

Have had hot water off since 6pm last night and the hot spot is gone. So 90% sure it's a leak.

Looking at the diagram which one is the line in the attic?

If it is the one going from the outlet on the water heater to the sink that is just below the hot spot then this is what I would do (and have actually done before calling a plumber).

See if you can see the pipes behind the sink (if they left the sink base cut open) and even better if you can reach them. Turn the hot back on and see if you can tell which of the 2 pipes going into the slab is getting hot (meaning it's leaking. You may want to run the hot water to the sink for a little bit to speed up the process.

If you can't see the pipes but are sure that they ran pex from the water heater to that sink then I'd carefully cut a square out on the wall in the opposite room to expose the pipes (probably a 12" x 12" or larger). You will do a lot neater job than most plumbers. Being neat means you can put it back in easier.

Then you can figure out which pipe going into the slab has the leak by feeling if it is hot.

That will make it easier for a plumber to come in and assess the situation.

If you are handy then after identifying which pipe has the leak you can cut a small section out and put a cap on both sides and then use the hot water in the kitchen.

Once you watch the plumber dot their thing you'll probably want to tackle the next one yourself. I bough a bunch of Pex pipe, fittings, and the crimper last year during the freeze just in case any of my lines burst when they thawed out.

If you have a plumber out to fix this one ask him for a repipe quote. Unless it's your forever home I think you'll have sticker shock (I know I did).


One last thing if your pressure going into your house is really 62 PSI from the city then your pretty good. If it's a lot higher consider a Pressure Reducing Valve.

Wait….

You said you killed the hot water and the hot spot is gone. Great. Now turn the hot water back on and see if the spot returns without anyone ever using a single hot water source anywhere on the side of the house. I'm not convinced.

Have done the shut off and turn back on of hot water twice now. Have used all hot fixtures as normal and hot spot hasn't returned yet. I don't get it. Why would it be hot for such a long time and not come back ?

Also isolated the line from under sink that goes through slab to master (the one I think is leaking). Luckily the drywall was already cut out so easy to see everything.

We can do testing to determine where the leak is and then reroute that loop, assuming your manifolds are above slab as they should be.

We have experienced plumbers in San Antonio.
Message me if interested.

GCRanger said:

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Have done the shut off and turn back on of hot water twice now. Have used all hot fixtures as normal and hot spot hasn't returned yet. I don't get it. Why would it be hot for such a long time and not come back ?

Also isolated the line from under sink that goes through slab to master (the one I think is leaking). Luckily the drywall was already cut out so easy to see everything.

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That's what I thought. Now, if you go use the hot water for a bit, I bet it returns. I'm thinking you don't have a leak but rather a spot that just transfers heat easily. If you are using the hot water, then that area has continuously hot water running through it. When you shut it all off, that spot goes cold. If it was a leak, I personally would think it would still be hot.

Look at water meter and see if it is moving.
If it is, turn off the valve at the water heater. If it stops then you have a leak on the hot side.

Parents house had this exact same issue a few years back but it was in their kitchen right in front of their island. They re-did their floors about a month later and while removing the tile they had the contractor carefully go over that area to see if there was any moisture or anything in the area under the tile.

It's a good thing they were careful as they figured out the hot water line wasn't properly seated when the slab was poured and it had floated to the top of the slab. It was fully encased in cement but after sanding and scoring for the self leveling cement pour, you could see a glimmer of the copper plumbing line.

No leak or anything. Just whenever they use hot water throughout the house, they have a 6" by 3' strip of heated floor for anyone who wants warm feet in the kitchen.

I initially noticed the warm spot around 3pm on a Thursday and it was still warm (75 degrees vs surrounding tile at 69-70) Friday morning without any hot water running for a long time (no baths or showers). After I turned off the hot water it eventually cooled off to the ambient floor temp. We've run the household as normal the last couple days (showers, baths, dishwasher, loads of laundry) and it hasn't heated back up at all. I'm stumped as to cause since it hasn't come back, whether a leak or pipe near surface.

Checked the water meter and ran multiple tests and the leak spinner never spun but did move just slightly over time. Put water pressure gauge on hose bib and shut off main and the pressure dropped about 4 PSI but then stabilized. Ran that test twice with same result.

I'm stumped.

It has motivated us to start planning out our bathroom remodels. Anyone have good contractors in SA we could get bids from? We may do some of it ourselves to save money.