FreshFish

My water bills were too high so I checked my meter and found that the leak detection dial was spinning (ever so slowly - in fact it was more like it would be still...then build up enough to spin a tiny bit, and then repeat). I do not know where the main water shutoff to the house is, but I tried turning the water off at the water heater and BOOM the leak stopped. So that told me it was either in the hot water pipes or the radiant floor heating system (which covers a good 80% of the house).

Now the floor heating system is typically a closed system, unless it needs to pull additional water in (if the system is drained for maintenance, etc). I called the company that installed the floor heating system because the plumbing in the water heating closet is super complicated. They supposedly isolated the system from allowing any water in (turning it into a closed system basically) and the meter continued to run. This tells me it isn't the floor heating. I should also mention that there is absolutely NO signs of any water in the house anywhere, with the exception of a musty smell in one bathroom...more on that later...

I deduced that it must be in the hot water plumbing somewhere. The problem is that my house has been pieced together over the years and has a combination of slab foundation, a 'crawl' space, that is really about 10" deep (groan), and about five different roof lines, two of which are not accessible. My problem now is that I don't know where the plumbing lines run for the 10" deep crawl space side of the house. I have already cut two holes in the floor and three holes in the wall to trace pipes from various sources, but no moisture anywhere. I can see about 1/2 of the hot water pipes under the bathroom mentioned above, but again, no moisture whatsoever. I am going insane.

Sorry for the rant. I have two questions:
1) Is there any way that I can confirm my hypothesis that the leak is in my hot water plumbing. I dont want to waste my time looking if I can rule it out.
2) Is there anything obvious that maybe I am not thinking of? The water heater is BRAND new (replaced after I initially found the leak, but the leak continues). I have checked my faucets for drips and see nothing odd.

nealtw

Do you have plumbing embedded the the concrete slab anywhere near or in the wall above the void in the fill below.

FreshFish

No
I was initially convinced that my void must have been related to this leak, but I can't find any evidence that plumbing runs under the concrete slab where the void has formed. I also looked into the void on a dry day and the soil in there doesn't look particularly moist.
The room over the void has plumbing in the wall (you can see the hose bib in one of the pictures) that runs to the adjacent room, which is a bathroom...but I cut into the wall and the pipes look totally fine in there. No sign of water. The bathroom is where the pipes run under the floor in the ~10" 'crawl' space. I am struggling to find how the pipes get from the bathroom to the water heater, which is why i have been creating so many holes...

I was really hoping there was some test I could do to make 100% sure it's in the hot water plumbing rather than the floor heating system.

Either way, it's soooo frustrating that I can't find any evidence of water anywhere. The meter reading tells me it's about 30 gallons/day leak.

woodchuck

I assume a new pressure relief valve came with the new water heater but that's what what the leak seem to be like. You'll have to look where the valve sends the water to check this.

isola96

After reading this my suggestion is to get a plumber out there to look, your supply is town/city how far is the meeter from the house? Could be right at the meeter.
Your T&P valve isn't blowing off or leaking so leaves you with slab or in the wall or at meeter.

Get a plumber in there to look.

nealtw

That much water should not be hard to find, I agree with isola about a plumber.

ozone

You state the majority of the home is serviced by a hot water system. By chance do you have a secondary forced-air system with a humidifier? If so they are usually plumbed to the hot water supply side.