External vs Internal sources of water leak in my concrete floor??

FreeBear

stuart45 said:

If you think your central heating pipes are leaking, and you have a header tank in the loft, tie up the ball valve and see if the water level in the tank drops.

Or if it is a modern boiler (combi or system), monitor the pressure - If it constantly needs pumping up, that could be an indicator of a leak.

Make & model of the boiler ?

gutovicky

Thank you everyone for the tips and advice...

Yes stuart45, I'll try to do the 'tying up ballcock in header tank' thing...   though it may be difficult to reach...
The CH header tank will be the SMALLER of the two tanks in the loft, correct?

No FreeBear, my boiler is neither a Combi or System; it's a 'normal' boiler (open-vented, with hot-water tank) - though it is new.
The gas boiler and the radiators were all replaced in 2017...   but NOT the pipework buried in the concrete!!

As an aside, since my old CH system (Baxi Back Boiler) must have been 30-40+ years old when the work was done, do you think it was reckless [of the company doing the work] not to have renewed the radiator feed & return pipes (in the concrete) at the same time??

Cheers, Vicky

stuart45

Yes, your header tank will be the smaller.one.

FreeBear

gutovicky said: The gas boiler and the radiators were all replaced in 2017...   but NOT the pipework buried in the concrete!!

As an aside, since my old CH system (Baxi Back Boiler) must have been 30-40+ years old when the work was done, do you think it was reckless [of the company doing the work] not to have renewed the radiator feed & return pipes (in the concrete) at the same time??

Reckless, no.

They could have done a pressure test of the pipework, but five years ago, there may well not have been any indication of an impending leak. That said, if they had experience of problems associated with buried copper pipes, they could have advised you to replace/reroute the pipework. This would have added quite a bit to your bill and created additional upheaval in the process.

stuart45

If it's only leaking in one place, you might be able to fix it. The pipes usually sit on top of the concrete slab, and are covered by the screed.
As the slab probably won't be perfectly level, water from a leaking pipe will often pool more in the dips on top of the slab, and come up to the surface there. 
I helped a friend of mine trace a leak last year. He just had to break up some of the screed, and repair the pipe.
There is always the chance that it's gone on a few places, and it's easier to replace the lot.