[Closed] Finding a water leak under concrete floor

Thermal camera?

Probably under the concrete as a ‘strong’ concrete mix can cause copper pipes to corrode. Might be simpler to just run new pipes as skirting level downstairs rather than digging up the floor?

Could you confirm which section of the heating system the leak is in, by isolating the pipework that runs under the concrete floor, before going any further? If it is still leaking with the bits under the concrete isolated then you know the fix is going to be in the "accessible" bits; if not then it's time for some new pipework to the sections currently run through the concrete.

PS. we had pipes for our kitchen and bathroom in concrete floors when we moved in. When I was putting in the new kitchen it was much easier for me to just re-do all the pipework for the kitchen and bathroom (including putting in a new false wall to cover it all up) that it would have been to do anything to the pipes that were in the floor.

Ive a big sds abd selection of chisels in the garage...
So thermal cameras might pick it up if you wind up the ch temp and let it run for a day, otherwise start with the lowest hanging fruit, the carpet areas lift and look
Then its tricky, you might end up running a 22mm ring up in the ceiling and dropping down to each rad with 15 either sirface mountbor conduit or buried in the wall, or it's possible to chase out behind skirting boards and hide the pipes back there, not hard job but veru time consuming
I wish you luck with that.

Could you confirm which section of the heating system the leak is in, by isolating the pipework that runs under the concrete floor, before going any further? If it is still leaking with the bits under the concrete isolated then you know the fix is going to be in the “accessible” bits; if not then it’s time for some new pipework to the sections currently run through the concrete.

Possibly even rerouting it. Everything leading to and under that floor gets diverted to go around it.

Just been wandering around with the thermal but struggling to keep the water in the system long enough to get it hot. Plumber coming back later so will be looking at options to isolate sections and narrow down the search - but limited options here as the whole ground floor is concrete slab and I think it will be impossible to isolate rooms for example. Almost certain it's downstairs too as the amount of water we're losing means an upstairs leak would make itself known pretty quickly.

No low hanging fruit unfortunately - getting anything up is going to be a monumental ball ache.

I think some home insurers offer a trace and access service? Let them figure it out?

Could you fill it with radioactive isotopes and use a Geiger counter?

Got a compressor?
With a bit of pipe and jubilee clip you could blow air into the system
Air is less dense and will leak faster than water at 1bar.
Then a metal rod in your ear and you might just be able to hear hissing when the compressior isnt running

What a massive ball ache!

Pressumably all you can get to of the pipework is the radiator tails, which is basically useless for diagnosis.

I used to do gas tracer testing on floor slabs, which was to check that the underlying barriers were intact. It involved bottled helium and a special detector. Wildly sensitive and not much stops helium penetrating. Certainly not concrete.

If you could get one of them, pressurise the system with helium, that would find it.

Or find someone who can do it.

https://www.sewerin.co.uk/products/water-leak-location/variotec-460/

struggling to keep the water in the system long enough to get it hot.

Implies a good sized leak?

rod in your ear and you might just be able to hear hissing

Had an external leak once and the old guy who came to find and fix had a wooden pole with a knob on the end for just this purpose (I hope only for this purpose, excellent old tech either way...): press to the ground/pipe and listen. But actually, I guess that's looking for a mains pressure leak with some energy to force a hiss. You could try with the system running - easy but unlikely to hear anything; or rig something to get mains pressure water briefly into the under floor bit for a few mins - excessive for something that's unlikely to actually work.

(In fact now I think, we had this in the first place we bought - a rubbish 80s cut and run conversion of a London victorian terrace basement. But you could see the damp coming up through the screeded floor near a radiator, so clear where the leak was.)

There are plenty of people who do this for a living - get somebody in with a thermal camera and they will be able to find the leak in the concrete slab for you. Money well spent

I take it yiu have checked it’s not something simple like the boiler dump valve faulty ?

Bit more background to add to the puzzle...

The system used to be old fashioned, vented system with expansion tank in the loft. We had loads of problems before christmas with air in the radiators and had to keep bleeding them to keep the system running. It got worse to the point where we'd only get a bit of heat in a couple of radiators and the rest were cold. Felt like there wasn't enough oomph in the system to push the water into the radiators - the flow and return were getting hot at the boiler but no water making it up into the radiators themselves. 2 x plumbers reckoned that pressurising the system would sort the problem but I was reluctant as it's been running fine (we have to assume - only bought the place 6 months ago) for years and we weren't getting to root cause.

Anyway, no other realistic options so plumber pressurised it yesterday and it ran lovely for a few hours (as it does after a full drain and refill) then pressure in system dropped from 1.5 bar to 0 in a few hours. Lying in bed last night we could hear air gurgling into the radiators in big slugs every few minutes as the radiators were draining.

So yep, decent sized leak!! Not a massive house (3 bed) but quite long and thin so some decent runs of pipework that will hold a fair bit of water. I can't believe there is no evidence of a leak anywhere.

Checked insurance policy and won't be covered as normal wear and tear clause in there.

Then its tricky, you might end up running a 22mm ring up in the ceiling and dropping down to each rad with 15 either surface mount

Our 60s house had a single pipe system i.e. no flow and return. Rather than dig up the whole ground floor we did exactly this - new flow and return circuit upstairs by lifting the floor (6'x4' 1/2 ply, so not easy in itself). Drops are mainly behind or in cupboards or via the garage, all boxed with covers held by screws so we can access if necessary. Looks fine now it's been decorated.

I would have thought that if it's losing that much water it would still show as a damp area in the concrete as the CH pipes won't be that deep and it seems the leak has been there for a while.
What's the floor covering?

My sister had to replace (under insurance) a wooden floor that was over a concrete base - the CH pipes sat in a small space between the concrete and the wooden floor and the concrete has corroded the copper allowing a leak that caused the wooden floor to warp.

Big stone tiles cover it in the kitchen, mix of wood floors, some carpet in the rest.

I'd also have thought we'd have smelt a bit of damp (effectively no heating in large parts of the house for a month and a continued leak) or seen damp spots on wood floor etc. It's a bloody mystery!

Presumably the vented system kept topping itself up, which explains why you didn't notice such a massive leak until you pressurised it? Is it possible that pressurising the system could have made things worse? Just wondering if there is a way around the wear and tear clause in your insurance as it sounds like it could be quite an expensive fix for you.

It was probably fine until it got pressurised - that'll just open up any pin holes and weakness in the pipes & rads.
Had a similar problem when I switched to a combi in my first house - although it was the rads that were the issue and not the pipes.

Yep, I'm sure that pressurising it has made it worse. It was probably a tiny leak before but we've never heard the rads actually gurgling and draining like we did last night! Which makes me think pin hole / corrosion that's been blown open a bit. It was probably only under about 6m of head (downstairs) on the vented system and that's only about 0.6bar. It's now 1-1.5bar (when full!).

It was probably fine until it got pressurised – that’ll just open up any pin holes and weakness in the pipes & rads.
Had a similar problem when I switched to a combi in my first house

+ 1 - same here - within 3 weeks of getting a combi fitted and pressuring the unpressured system the underfloor PEX started to rupture ..... REplumbed and its been fine for 10+ years

PRessuring it was probably the worst thing to do but tbh you had an issue and the solution is the same presssured or not.

So if the leak was inadvertently made worse by pressurising the system, is it worth talking to the insurance company to see if they will cover it or would it still be classed as wear and tear? I can understand why they might say wear and tear, but it's gone from un-noticed to pretty catastrophic quite quickly so there might be an argument for insurance to cover it?

So if the leak was inadvertently made worse by pressurising the system, is it worth talking to the insurance company to see if they will cover it or would it still be classed as wear and tear? I can understand why they might say wear and tear, but it’s gone from un-noticed to pretty catastrophic quite quickly so there might be an argument for insurance to cover it?

having gone through insurance last year on a leak under slab - most policies have a hefty excess on internal escape of water

I had to argue the toss as our mains (pre stopcock) pipe burst(froze in -19) last year and saturated our slab / laminate/ plasterboard

they claimed it was escape of water internal as it had damaged the house aand i was liable for a massive excess - i had to prove it was the mains line comine to the house that had failed - which was easy as i had video of it burst which brought it back to 500 quid excess

Still trying to figure out what's going on. Plumber here now isolating different parts of the system - there's an upstairs loop, downstairs loop and HW loop all with 50 year old (minimum!) valves so assuming they are working then currently not looking like it's the downstairs loop that's the culprit. Still work in progress though and fair chance the old valves are passing so not telling us much. Might replace them in first instance and then we can properly isolate circuits and find source of problem.

Sounds like a plan - you need the ability to isolate upstairs and downstairs as a minimum. May as well replace those valves to ensure they're working, then work from there.
(I would imagine the HW loop should be pretty simple)

Easy, but messy, just undo compression fittings down stream of valve. Open up the boiler, add a few psi and fire it up baby
You will find out very quickly if your valves are doing what the ought be

Edit, have you thoroughly checked the perimeter of your house for water
Chances are the ch fluid has hit the footings and could have soaked your geraniums enough to be wetter than the surrounding area, unless you live mid terrace, then your screwed

Rothenburg do a test kit. I sell them st screwfix, you need to know where this water is going amd this will help.
Or a trackpump, presure guage and a few jubilee clips.

As a leftfield suggestion for leak detection - how aboiut either some devining rods or one of those long sticks you put your ear to to listen for leaks, tha tteh water companies use?

Now you may all laugh )quite rightfully) at divining rods, as would I as an engineer, bit I have seen them used and used them myself to good effect, backed up with CAT scans and actual excavation.... Don;t ask me how it works, or how reliable it is, as I can see no logical explanation.  But if you're desperate, or want to explore every avenue, it may be worth thinking about.

I know I've just basically recommended Voodoo to find a water leak BTW, and i wouldn't rely on it solely, but I would definitely consider it as part of a range of options...

.Let the mockery commence?

Update!

So the plumber has isolated various circuits and we've confirmed it is the downstairs loop. Somewhere under the concrete slab.

Spoken to the insurers with this information and they won't cover the cost of the repair to the pipework itself - that's the wear and tear bit. And is, quite frankly, the cheapest part of the whole thing. What they will cover is specialist leak detection, cost of knocking holes in stuff to get to leak and then repairs to fittings and fixtures afterward. Bloody good result as far as I'm concerned.

Leak detection company coming out tomorrow with various options from thermal cameras to acoustic stuff and gas detection. Jeez, what a palaver!!

Great news, must be a relief to know you're not liable for the whole lot!

Great news on the insurance OP, keep us updated!

Probably under the concrete as a ‘strong’ concrete mix can cause copper pipes to corrode.

Metal pipes should be lagged before being buried in concrete as it will corrode them regardless of the mix.

Looking forward to seeing pictures and updates so I'm going to subscribe .....
Oh wait, I forgot where I was! 😩

Definitely one for your insurers.

The leak detection team will find it pretty quickly using gas detection & thermal imaging as mentioned above.

Apart from your excess and the cost of getting your plumber to repair the failed pipe, the rest should be covered.

Its worth thinking about renewing the remaining pipes (at your cost) if they're of an age where they are going to start failing frequently in the slab. Alternatively Dyno-Rod have a service where they drain the system down and fire sand through the pipes to abrade the inside face, then blow a powdery resin through that sets hard and lines the old copper pipes. Similar to traditional drain lining but works even on 15mm pipes.

I deal with EOW's all the time and I'd seriously consider renewing all of the pipes as even though your insurers will cover future losses, its the faff factor and disruption to your lives that I'd want to avoid.

I would re[pipe the system with above floor pipework.  solves the issue ad future proofs it.  Put the pipes behind skirtings if you are bothered about exposed pipes

if one has gone others will soon follow

This happened to us and I’ve tried to delete it from my memory bank. Happened just before my son was born so cute a very unhappy and cold wife for a week or so. Ours leaked in multiple spots which led to us replacing all ground floor pipe work. Given the routing overground options were very limited so cue water cooled concrete cutting inside the house. The vision of someone hosing down your walls is not something I wish to repeat. Insurance covered detection and replacement floor in one room but not the plumbing work itself. Since installation the heating has worked perfectly. Good luck!