Puzzle: When is a noisy mains supply pipe not a leak?

[diy_dan]

I'd really appreciate some advice.

Recently moved into house and quickly became aware of 'rushing' noise in pipes (sound like cistern filling) which never stops. Loudest around rising main stopcock and stopcock in upstairs bathroom. Not related at all to hot water or radiator pipes. Direct water supply - no tank in the loft.

Stopcocks in house are all fully open. Closing them reduces noise level, but does not get rid of it.

Thought it was a leak in mains supply pipe. this was backed up by plumber who came round. I also called Thames Water (because of complications with it being a shared supply pipe with neighbours - although they can't hear the noise and don't have any overflows, etc, going).

Guy from Thames Water with his listening device said it sounded like supply pipe was 'shot to pieces' as noise was so loud through the ground and at stopcock and mains stopcock in pavement. (although, as I pointed out, the water pressure has always seemed very good)

HOWEVER - after he turned the mains stopcock in the pavement (which unsurprisingly stopped the noise all together) and then turned it back on again, the noise had stopped completely. For the first time all was silent, even though the water was all flowing! He couldn't understand why this was. But we didn't care too much as it seemed that the problem was fixed and there clearly wasn't a leak....

... until some 24 hours later, when the noise returned.

What can it be!? Any suggestions?

 

[jumpeyspyder]

I know very little about plumbing but a fair amount about sound

maybe one of the experts could shed some light here - Could it be something in the pavement stopcock itself vibrating ??

Alternately maybe there is something else that is vibrating that is physically touching the mains supply pipe ?

hope this helps somehow

 

[ChrisR]

Have you or your neighbour got a water meter?
Did the water chap test for a leak?

 

[Slugbabydotcom]

What can it be!? Any suggestions?

An intermittent leak.

Ive never come across it but can imagine a scenario where a joint that hasn't been made too well is pushed apart by the pressure. When the pressure stops the elastic strength of the pipe in its situation is sufficient to remake the joint sufficiently to stop the joint separating. that is until the pressure builds up and during a period of low use as the mains pressure builds up the joint separates again.

Rarer than rocking horse shiot I'd say but nevertheless plausible and possible.

Please post back and let us know when you do find out what it is.

 

[BoxBasher]

Sorry for the long post, but I can hopefully pass on some useful nuggets of leak detection here...

Could be a leak, could be one of your neighbours drawing off (if you are on a shared supply). Also as Slug says, could be intermittent due to flexion in pipes with pressure differences. Also at low demand times, pressure build up will make a leak push out more water, therefore increasing noise.

With regards to proving if there is a leak on your supply pipe, listen to the tap itself, either by pressing your ear flat against it or use a wooden spoon, handle on the tap, spoon part against your ear. A leak noise (especially on metal pipe) will sound like a combination of water flow and a fridge motor running (assuming that it isn't a fridge motor). you can also listen outside to the stopcock in the footpath (although traffic noise makes it harder to hear) Press a broom handle down on the stop tap in the box outside, then press your ear against the top. It can take a trained ear to hear it, but big leaks are easy to hear. You can also throttle the tap down, so that any water passing through will have to force through the jumper, increasing any noise.

If there is a noise, completely close the tap. If it stops then the leak is on your property, if it stays on then it down to good old Thames to come and investigate one of their many leaks.


Another way to test for a leak is to do a siphon test. If you have a kitchen tap that can have the end of the spout submerged in a glass then it is easy. Draw off a full glass of water (to the brim). Close the tap, then go outside and shut off the main stop cock (in footpath). Go back inside, open the cold kitchen tap and lift the glass up so the end of the spout is under water. If you have a leak then the tap will "take a drink", may be quick, might be slow. Faster it goes, bigger the leak. This will only work if your internal stop tap doesn't have a loose jumper, and there is no check valve between the tap and the underground supply.

This doesn't always work, but if it does there is probably a leak.

If you don't turn up with a leak, it might be worth asking Thames if there is a Pressure Reducing/Management Valve on the distribution main outside. These make a hell of a racket when operating (which is nearly all the time) and the noise will transfer through any pipe you have. Possibly even a partially shut valve or a "choke" in the main (which can happen with old cast iron mains). Sometimes noise from leaking mains can also pass into a house.

 

[BoxBasher]

From actually reading your OP properly (as I usually do eventually).

If the Thames guy shut your MST (mains stop tap) and the noise stopped then it's a prob somewhere with your plumbing.

You said if you partially shut your internal stop taps (IST's) then the noise reduces, if you shut either of the IST's does the noise stop?

Check any overflows to see if they are flowing/filling, especially one that discharges down pan as they are usually less obvious.

What age is your property? Did it or does it still have outside lav? Could be a leak on the supply/feed to this which may be controlled by your internal tap.

Could be where a lav was removed and the lead was hammered shut instead of the deadleg being removed and capped properly., can force open under pressure. also if one of your neighbours has had their own supply installed and either not capped off their old branch properly, or even still on the old common too, which would mean water circulating in though one feed and out through yours...

Noise will fluctuate at different times for reasons mentioned by slug.

Give it some thought then get back to let us know...

 

[pannierstan]

have you got a swimming pool in the back garden which is getting bigger by the day

 

[diy_dan]

Guys - thanks for your replies. Really appreciate the interest and help!

I haven't had a chance to do any further investigation yet, but will try some of your suggestions this weekend.

Chris R - Neither of us have meter. The only check he did was listening. So when noise stopped he concluded it wasn't a leak (for 24 hours there was no apparent problem at all).

Slug - sounds like it could be an intermittent leak. Would be possible and would explain.

Box - thanks for siphon test suggestion. I'll give it a go this weekend.
- And when i close ISTs fully, noise reduces, but doesn't stop.
- Can't find an overflow going anywhere (checked the pans!) Neighbours say they haven't got anything overflowing either. But I only have their word for it - don't really know if they've checked. When I went round, we couldn't hear the noise coming from their pipes.
- Victorian, but no outside lavs. All originally had bathoom and lav at back of kitchen. I and neighbours still have lav there.

I'll update on what happens - but I think I might have to get Thames round again for further investigation.

 

[BoxBasher]

Is the feed to your lav underfloor or is it above ground?

Chasing an underfloor leak can be a right ball ache...

I would certainly try isolating at MST again first, to see if you can stop/start the noise... if it does turn out to be your leak, and you do get Thames out again, they might end up telling you to get the whole pipe replaced.

see
http://www.thameswater.co.uk/UK/reg...ow_000224.jsp?SECT=General_Image_Below_000224

for Thames policy on leaking shared supply pipes.

 

[wilhelm]

maybe its turbulence at your stopcock in road. and your rising main is acting as per this....

who knows?

 

[geoff@cetltd]

Aliens

 

[diy_dan]

Grr, still not getting anywhere with this.

If it was turbulence at stopcock in road, how could I test this? Any suggestions for what to do to get it sorted? Would it only be me experience the noise or would others?

It seems wither something up with stopcock at road, or a leak which magically 'fixed' itself for a few hours. Not sure which I think seems most likely!

Thanks for all the suggestions so far!

 

[diwoman]

'<<rushing' noise in pipes (sound like cistern filling) which never stops. Loudest around rising main stopcock and stopcock in upstairs bathroom. Not related at all to hot water or radiator pipes. Direct water supply - no tank in the loft.

Stopcocks in house are all fully open. Closing them reduces noise level, but does not get rid of it.

Thought it was a leak in mains supply pipe. this was backed up by plumber who came round. I also called Thames Water (because of complications with it being a shared supply pipe with neighbours - although they can't hear the noise and don't have any overflows, etc, going). >>>

diydan-I have had this identical in every detail for 20 years.
Same thing with the Water Co..
no damp or water around.
They threatened to cut us off for years, but when I enquired about their offer for a new connection, they give us the brush off ; and the shared house is rented so cant share the cost or have it done at all! So there iS such a problem! And there MUST be an explanation.
Can we contact you ? from [email protected]
<<Guy from Thames Water with his listening device said it sounded like supply pipe was 'shot to pieces' as noise was so loud through the ground and at stopcock and mains stopcock in pavement. (although, as I pointed out, the water pressure has always seemed very good)

HOWEVER - after he turned the mains stopcock in the pavement (which unsurprisingly stopped the noise all together) and then turned it back on again, the noise had stopped completely. For the first time all was silent, even though the water was all flowing! He couldn't understand why this was. But we didn't care too much as it seemed that the problem was fixed and there clearly wasn't a leak....

... until some 24 hours later, when the noise returned. >>>

 

[corgigazza]

Had something similar before in stevenage herts before, turned out that the pipe under the floor in kitchen & hallway was plastic and buried in concrete floor as u turned of stop cock in house the niose went away, the water was washing away the foundation sand and going into the out side drain in fronf of kitchen a new water run was needed to feed upstairs, after capping feed under floor.

 

[Agile]

Had something similar before in stevenage herts before, turned out that the pipe under the floor in kitchen & hallway was plastic and buried in concrete floor as u turned of stop cock in house the niose went away, the water was washing away the foundation sand and going into the out side drain in fronf of kitchen a new water run was needed to feed upstairs, after capping feed under floor.

But that could not have been leaking because Softus says plastic pipe never leaks!