Leaking heating

[Keithj]

The central heating didn't come on yesterday morning. This was a major domestic disaster.

Investigation revealed the pressure gauge at zero, so the system was duly topped up to 1.5 bar, and the heating came on ... and stopped a few hours later when the pressure was back to zero. We have a leak. The problem is, we don't know where the leak is. It's not anywhere visible, or where it shows in puddles or damp patches or smells, so I conclude it has to be in one of the pipes under the downstairs floor (all the other pipes are visible, or would make a visible puddle if they leaked).

Our local plumber has been, looked, agreed the diagnosis, and suggested it might be best if I did some more investigation and found where the leak is. He'll do the job (for a fee) if I ask him to, but warns that looking for leaks can be a messy and an expensive business.

Has anyone any useful tips on how to find such a leak? The pipes from the boiler go under the floor immediately, so I can't turn off individual branches of the system.

 

[Flyfisher]

I suppose it depends on how deep the pipes are under the floor but I've heard of thermal cameras being used to look for leaking pipes. A quick google found this http://www.inlec.com/environmental-testing-equipment/leak-detection-flow-meter-c220/palmer-environmental-under-floor-leak-detection-kit-p379

The same search also found this http://www.findaleak.co.uk/leak-detection-equipment.html
I've no experience of such things but there seems to be many different techniques that could help . . . All at a cost no doubt but it might be worth some phone calls to discuss the options.

The only other thing that springs to mind is to isolate the underfloor pipes one at a time and temporarily re-route them on the surface using plastic piping. If all the buried pipes follow the same route then this won't help to locate the actual leak though it might be a useful way to quickly, if temporarily, getting the heating working again and buying time to locate the leak with less urgency. Though this option is probably not practical if there are many sections of buried pipe work.

Not a nice problem and none of the above will avoid the eventual need to dig up the floor anyway.

 

[Lime]

Has anyone any useful tips on how to find such a leak? The pipes from the boiler go under the floor immediately, so I can't turn off individual branches of the system.

What type of floor is it?
Usually the leak will be at a joint and most will be near radiators just where the pipes drop.
A hand down a hole feeling the joints will discover a leak far quicker than anything visual.

 

[MdB]

I've heard (no pun intended) that stethoscopes are commonly used to listen for the hiss from small leaks and that it works through floorboards. Sounds (no pun intended) reasonable to me but it isn't something I've ever done.

 

[middi]

Good question from LIme- What kind of floor is it, concrete or timber with void.

If timber with void, you have to gain access to the void an with a torch look for signs of leaks.

If concrete, the water leak is usually manifested by travelling along the pipe run and the concrete where the hot pipes enter into it shows signs of wet.

Middi

 

[robgil]

It could be the pressure release valve on the boiler expansion vessel.

 

[Baron de Gynes]

Or alternatively it could be that the diaphragm in the expansion vessel itself has failed; they are only rubber after all.

That's what was the matter with ours last winter. It was a cold, cold winter...

 

[FamilyWiggs]

DO you have an idea of the volume of water being lost? ie how much you are filling it up with?

It strikes me that to go from 1.5bar to zero in a short space of time is a significant leak and that kind of volume would be pretty obvious. Might it be more likely it is being lost into the expansion tank as suggested above? That would certaily be preferrable to digging up the floor....

 

[MdB]

It strikes me that to go from 1.5bar to zero in a short space of time is a significant leak and that kind of volume would be pretty obvious

If the system hasn't been bled for a while, it could be a few litres but if it has been bled, the amount lost could be quite small. Water is non compressive (unlike air) so it doesn't take much to change the pressue.

 

[Keithj]

Thank you all!

The amount of water being lost isn't much - I would guess that from 1.5bar to no bar is less than a litre of water. I've not measured it, but it's a very few seconds with the valve open to repressurise it.

I've bled all the radiators, and there is no air in them. There are no signs of damp round any of the radiators or pipe runs - we've checked them pretty thoroughly.

The floors are a mixture. The kitchen floor is tiles, probably fairly modern. I suspect that it's screed or earth underneath (but haven't burrowed down). The other rooms are oak (modern, rather like laminate in construction, but solid oak). Under the bits we disturbed while doing the repairs, it seemed to be screed.

The new build (which has one radiator and one towel rail fed off the main system) is screed over Celotex over suspended block & beam.

Colin the plumber assures me that the expansion vessel is in good order - it should be: it was replaced about a year ago (not by Colin).

I like the stethoscope idea - I have one somewhere in the workshop. I'm not too hopeful, because the leak rate isn't all that high so may not make a noise.

We've tried walking round in bare feet looking for warm patches on the floor. No luck so far.

I suspect we're in for a man with thermal imaging, which I understand is £500 for a visit but they guarantee to find the leak.

 

[philpjuk100]

A stethoscope (or a piece of dowel)works well on mains pressure but I doubt if it will pick up a leak at heating pressure.Good luck, phil.

 

[Lime]

Have you had any carpets laid recently?
My inlaws had a carpet laid in their new house and almost immediately water was coming out of the outside wall via the damp course.
A nail had penetrated a pipe.
From then on I referred to the house (which I disliked intensely) as HMS Oakwood.

info. The house name was Oakwood so called after the trees that were cut down for it to be built.