Filling Loop: leaks

2 Jan 2007
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United Kingdom
Hi I posted on Friday and was looking for a bit more info.

I have been having problems with my CH sytem. Have discovered that I have a leak in the pipes in concrete. Concrete has been dug up where there is a damp patch (in my bedroom, which is the room next to the kitch (where the boiler is) and I have now have a fairly large hole there. The engineer expected to find the CH pipes here to be leaking. However, the CH pipes are all sound here, although concrete is wet.

When I turn on the filling loop, after about 10 mins, I get a large pool of water in the hole. Obviously there is a leak and the water is settling here. When I eventually manage to re-pressurise the system (it takes about 20 mins) there is obviously a substantial amount of water in the hole.

Whilst the heating is on, the pressure is maintained. When heating goes off and pipes cool, I lose pressure and hole in bedroom fills up with water. I have a couple of stupid questions (!):

1. How does the filling loop work? Presumably water is drawn off the mains and fed into the system. From looking at the pipework, the filling loop appears to be fitted to the DHW outlet pipe and the CH flow pipe. Is this correct? As the leak happens when I turn on the filling loop and the pipes are cold, what pipe is likely to be leaking (CH flow/DCW?)?

2. When the system is re-pressurised (and filling loop is off) and heating is on, the system maintains its pressure. When system is cold, it loses pressure and the hole fills up with water. What I know for sure is that the water ends up back in the hole through a leak, but presumably the water is leaking from the same pipe?

What I really want to know, is it possible to determine from the above information which pipe in/from my boiler is likely to be leaking , bearing in mind that the build up of water in the hole starts when the filling loop is on, stops when the heating is on, and starts again when the heating is off? Also, is there likely to be something wrong with my filling loop (in addition to the leak)?

My insurers have aleady dug up a large part of my bedroom and we are no closer to finding the leak, so any info greatly received!

Thanks a lot and sorry for the ramble.
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The leak is on the heating pipes.

How to find it is easy with half a brain and a bit of luck.

From the small quantity of water you are loosing coupled with the fact it only leaks when cold, all you have to do is find a joint (tee)

You should be able to roughly chalk the pipe runs on the floor using the radiator tails as a guide.


When the system is cold and up to pressure check the radiator tails for signs of water running down the pipe :eek:

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