Small leak under slab

[Ladd Borne]

Hi. I happened to buy one of those pressure gauges that hooks to hose bibs and decided to see if I had any leaking toilets, etc. I hooked it to the utility sink faucet and eventually determined that I must have a small (1 cup per hour) leak in a hot water line under the slab.

I isolated both cold and hot and the leak is only on the hot side. There are no visible leaks under any sinks, nor are any places wet. I've checked everything I can without tearing into walls or floors, including the hot water heater, dishwasher, washing machine, etc. So the leak must be under the slab. I've checked with an IR thermometer all over the floors and can't find any hot spots.

Can such a small leak be found by a local plumbing company?

Thanks

 

[CountryBumkin]

There are companied that specialize if finding under slab leaks, such as http://www.americanleakdetection.com/slab-leak-experts.php
Just Google "under slab leak detection" or similar wording and add in your state and city.

 

[Sponsor]

 

[Reach4]

Hi. I happened to buy one of those pressure gauges that hooks to hose bibs and decided to see if I had any leaking toilets, etc. I hooked it to the utility sink faucet and eventually determined that I must have a small (1 cup per hour) leak in a hot water line under the slab.

I think you are saying you are calculating a leak rate based on a pressure drop in the isolated piping. What happens to the pressure when you turn the WH back on?

 

[Ladd Borne]

I think you are saying you are calculating a leak rate based on a pressure drop in the isolated piping. What happens to the pressure when you turn the WH back on?

Yes, I calculated the leak rate based on pressure drop. I did not turn the WH off electrically - just shut it off from the cold incoming so that I could isolate the hot and cold lines to see which had the leak. No pressure change over 1 hour on the cold side, but there was a drop when testing the hot lines. When I turn the valve back on to allow cold water to flow to the WH, the pressure goes back to normal. Hope that answers your question.

By main question is can such a small leak be found? A couple friends had the same issue, but the leaks were much more evident in larger water bills. One had his re piped through the attic because they did not want to chase a leak in the slab as it was an older house. They other had his floors torn up, only to discover the leak was just outside the slab.

 

[hj]

A "Good" leak detector, not one who just has a stethescope or infrared device can find the leak, or just wait a few weeks until it gets bad enough to heat the floor or drain all the hot water from the tank.

 

[Dj2]

Nowadays, they have instruments to detect an under the slab leak, inches from the source. The cost is around $250 - money well spent.

HOWEVER, if you have copper lines under the slab, this could be a bad sign. Most under the slab leaks eventually lead to an inevitable re-pipe job. Why? because an underslab copper pipe will develop more pin holes in the near future.

 

[Reach4]

Yes, I calculated the leak rate based on pressure drop. I did not turn the WH off electrically - just shut it off from the cold incoming so that I could isolate the hot and cold lines to see which had the leak. No pressure change over 1 hour on the cold side, but there was a drop when testing the hot lines. When I turn the valve back on to allow cold water to flow to the WH, the pressure goes back to normal. Hope that answers your question.

Does the pressure continue to fall about the same percent in the second and third hour?

 

[Jadnashua]

Depending on the type of system you have (closed or open) and how recently you'd run any hot water, just the act of the hot water cooling could cause the pressure change. How did you isolate the hot and cold? Shut off the cold inlet to the WH? If you shut the inlet to the WH off, and do not have a closed system, you created one, and the pressure will change with temperature variations...down as it cools, up as it warms. Is there an expansion tank in the system (an indication of a probable closed system)? Without one, pressure drop could be entirely normal and is not an indication of a leak depending on the temperature change.

The real indication of a leak is the water meter moving, not a pressure change, unless it gets WAY low.

 

[Ladd Borne]

Depending on the type of system you have (closed or open) and how recently you'd run any hot water, just the act of the hot water cooling could cause the pressure change. How did you isolate the hot and cold? Shut off the cold inlet to the WH? If you shut the inlet to the WH off, and do not have a closed system, you created one, and the pressure will change with temperature variations...down as it cools, up as it warms. Is there an expansion tank in the system (an indication of a probable closed system)? Without one, pressure drop could be entirely normal and is not an indication of a leak depending on the temperature change.

The real indication of a leak is the water meter moving, not a pressure change, unless it gets WAY low.

Sorry for the long delay in getting back. Yes, the pressure had dropped from around 60 psi to 30 psi - too much to be accounted for with just temperature change. However, I eventually found the leak in a solder joint. Had to open up a wall to one of the bath tub faucets. The leak was dripping onto the slab but then going through the hole where the drain for the bathtub comes up which let it seep into the ground which is why I dismissed it at first because there was no sign of water around basedboards or drywall. Thanks all.