Major water leak in central heating system

[Burnerman]

This sounds like a massive repipe job then - what a shame!
I reckon, for such a volume of water to disappear, the pipe with the burst must be in an air void somewhere, allowing the water to disappear.
So, are you going to repipe on the surface, or start breaking the concrete out? Your main flow and return to / from the boiler terminate in things called 'manifolds', if its microbore - then the flow and return to the rads branch off from there. I guess the leak will be in one of the boiler pipes.
Lets know how you get on.
John

 

[Axel]

We never found exactly where the leak was - we ran a new pipe above the concrete floor level and disused the old one!

Before excavating, you need to be ABSOLUTELY SURE of which section the leak is in, so draw a diagram of the most likely pipe runs and try to isolate sections one at a time wherever there is some access to some of the pipes below floor level, by means of cutting the pipe and capping at various different points. This would minimise the amount of excavation. In some respects, the concrete is the easier bit, as it's not such a job to repair, but where there are tiled floors, that is obviously a headache. If it's carpet and you aren't planning on some original stripped floorboards one day, then that's relatively easy to access.

Just a thought - what with all this freezing pipe weather, is there a drain valve exposed outside? Sometimes a pipe is run out through the wall below internal floor level but above outside ground level, with a drain cock on it for the purpose of draining the system. If this had frozen and burst, then that would be the leak!

 

[jvn01]

Thank you for all your helpful replies. Here is my latest update!

Lifted the inspection cover to see if the water is somehow getting in the soil pipe, but no joy there.

Then tried John's suggestion and filled the header tank up to the overflow, turned the house water off, got someone to release the water in the header tank and listened for water.

I could hear water running in the suspect area, but wasn't sure if this was just normal flowing down the pipe or whether I could also hear a leak.

So I returned to the suggestion that you gave earlier and enlisted help to get behind that corner cupboard. Eventually managed to totally expose everything in that area. No pipes running down alongside the SVP and no sign of dampness anywhere. Excavated about 3" into the concrete where the central heating pipes were, but again no sign of damp.

At this I decided to throw in the towel on my investigation and got both these central heating pipes capped. The upstairs central heating and hot water now work (hurray), and I'll be asking a plumber to repipe the lower floor with pipework coming down the wall in the corners.

Failed in my role as Miss Marple!! But many thanks to everyone who tried to help me.

Mary Jane

Just to clarify - you said you heard water in the suspect area but weren't sure whether it was 'normal flowing down the pipe' - surely if you filled the tank and stopped it with a bung, then turned off the incoming mains, at this point everything everywhere should have been silent? If the running water noise restarted at the point the bung was released, wouldn't this suggest 'abnormal' water flow in that location?
Strange indeed...