Central heating system was leaking. Now cannot find leak.

JeffSouthgate · 9 Nov 2005

As part of extending the house, my builder added radiators to my existing central heating system. He used plastic pipes and compression joints to feed the new radiators. He laid these pipes on the new concrete sub-floor and covered them with a 3-inch sand and cement screed that finishes the floor. Over this he "floated" a solid oak plank floor laid on a plastic foam membrane. The heating system worked okay for a while, but then we got a loss of water pressure. It dropped one bar every twelve hours. No leaked water was visible anywhere in the house, so we assumed the leak was under the screed. We searched for it by isolating, in turn, each of two "runs" that feed the new radiators. But we only got a pressure drop of one-tenth of a bar in twelve hours. What might be responsible for the earlier big and constant pressure drops? Why has it apparently repaired itself? Can I trust this "miracle"? What ought I to do now? (Many thanks for any advice)

Agile · 9 Nov 2005

Leaks like this are actually through a very small gap. It only takes a very small piece of circulating debris to block the hole.

Since it was done by your builder, are you getting him to deal with it?

Were there any joints in the pipes under the floor screed?

Tony

JeffSouthgate · 9 Nov 2005

Agile said:
Leaks like this are actually through a very small gap. It only takes a very small piece of circulating debris to block the hole.

Since it was done by your builder, are you getting him to deal with it?

Were there any joints in the pipes under the floor screed?

Tony

Thanks for this, Tony. So if the debris moves away from the hole, it could leak again? The builder is doing his best to fix it, but, as you can see, the problem is a bit tricky. There are joints in the pipes under the screed, but only under the radiators, where the feed and return pipes are "Teed" off to connect with the radiator "tail" pipes.

There was no drop in pressure till the radiators were removed for the decorator, and then replaced. How likely is that to have "nudged" one of the tail pipes hard enough to open a compression joint in the screed below?

Also, the oak floor was laid snug round the tail pipes. No expansion space was allowed for the floor round the pipes, although space was left all round the room. The floor has moved slightly (it's a natural material). How likely could forces generated by the floor against a tail pipe open a compression joint embedded in the screed below?

Slugbabydotcom · 9 Nov 2005

As it happens I have just been reading up on this for a job I'm on with so the folowing extract from water regs was to hand

Location of water fitings

G7.1 Unless they are located in an internal wall which is not a solid wall, a chase or duct which may be readily exposed, or under a suspended floor which may, if necessary, be readily removed and replaced, or to which there is access, water fittings should not be:

1. located in the cavity of a cavity wall; or,
2. embedded in any wall or solid floor; or,
3. installed below a suspended or solid floor at ground level.

keego · 9 Nov 2005

Those reg's are for potable water but, do they apply to CH pipework?

Slugbabydotcom · 9 Nov 2005

keego said:
Those reg's are for potable water but, do they apply to CH pipework?

Application of Regulations
2. - (1) Subject to the following provisions of this regulation, these Regulations apply to any water fitting installed or used, or to be installed or used, in premises to which water is or is to be supplied by a water undertaker.

(2) These Regulations do not apply to a water fitting installed or used, or to be installed or used, in connection with water supplied for purposes other than domestic or food production purposes, provided that-

(a) the water is metered;

(b) the supply of the water is for a period not exceeding one month, or, with the written consent of the water undertaker, three months; and

(c) no water can return through the meter to any pipe vested in a water undertaker.

There you go Keego ... It seems like I have officially shot myself in the foot

I mean Er
Er full marks you found my deliberate mistake

Agile · 9 Nov 2005

Just a moment, if you examine the wording of that extract from the water regs you will see that they apply to all water pipes if the premises are supplied with mains water!

Actually its sloppy drafting as its only intended to be in respect of mains water supply pipes however as written it applies to all pipes.

If you then consider "good practice" then its NOT good practice to bury pipes in a screed. This is only done by builders and not by plumbers except in respect of continuous lengths of pipe for underfloor heating.

A properly made joint is very strong. If he used brass compression joints with plastic pipe then he should have used inserts inside the pipe to counter the compressive force. Some dont!

There is a leak sealer made by Fernox similar to the Radweld sold for cars. I would not use it myself as its "not professional" but I have heard that it sometimes works.

Tony

joe-90 · 9 Nov 2005

Maybe there was some kind of air void around the pipe in the screed which is now full of water - hence no more big drops? The water had to go somewhere and as you say there is no sign of it.
You are going to have to fix it otherwise it will seep up into the new wood flooring and it'll go all 'cupped'. It serves him right for putting joints under the screed anyway. The main attraction of plastic pipe is that you can buy it in a roll (so you don't need joints).

joe

JeffSouthgate · 11 Nov 2005

Thanks to you all for your thoughts on this. The plastic pipe under the screed is of the type called HEP. The joints are plastic compression joints. I share your concern that putting them in the screed has made it hard to inspect or maintain the pipe and joints. However, the builder assures me that it is accepted practice to do this, and that plastic pipes and fittings are designed to work okay under a screed. If he is mistaken, then what is the "professional" way to run central heating pipes in a house extension with concrete floors?

There is no sign of the water from the leak. It may have dropped down to the ground by exiting between the concrete blocks of the suspended concrete floor, rather than capilliaring up through the screed. Also, the oak floor is "floating" on a foam plastic membrane, so the floor might not warp unless the screed below the membrane gets wet rather than merely damp. How can we detect this water, so that we can find the leak?

chrishutt · 11 Nov 2005

Jeff said:
The joints are plastic compression joints.

No they're not. They are either brass compression or plastic pushfit. In any case they should not be buried in the screed. Contrary to the Water Regulations and just plain bad practice, for obvious reasons.

JeffSouthgate · 11 Nov 2005

Thanks, Chris. They are plastic push-fit joints.

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Central heating system was leaking. Now cannot find leak.

keego

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