Water pipe dripping sound behind wall

[Robert Thorpe]

Mystery noise;

I live in an old end terrace house. After using the cold water in the back kitchen there's a dripping sound that starts up in the front room by the partition wall where there is a stopcock in the corner, probably where an old sink used to stand beside the chimney where the front wall meets the side wall to the neighbours' house, and the sound is a foot or so above the stop tap. The sound seems like a heavy droplet of water dripping onto a hard surface about once every 30 seconds and gradually lessens after several minutes and stops. The wall here has plasterboard so I'm assuming there's pipework behind it running up. Above the front room is a bedroom. Where the sound is coming from the plaster and the paintwork is dry and the floor feels to be dry also. The sound isn't constant. The supply from the street to the house is lead and inside is copper piping. I've heard of hot water pipes causing sounds when they're heated but not aware if the water pipes can too, after using cold water, or whether this might be a leak behind the plasterboards?

Thank you for any advice.

 

[CBW]

Is the stopcock concealed?

 

[Robert Thorpe]

Yes, just above floor level there's a little cupboard box housing the stopcock.

 

[CBW]

Is anything wet inside there?

 

[Robert Thorpe]

No it's completely dry inside, the skirting and floor feel dry too as does the plaster.

Directly above the stopcock about waist height there's the noise of what seems like a drip hitting something for a while. I thought if it was a drip leak whether it might be soaking into wooden frames or insulation and drying only to come back when the water is used again. Unless cold pipes can actually make noise like this from contraction?

 

[CBW]

Any old drains that run that way, that could be causing the issue?

 

[Robert Thorpe]

Not that I'm aware I think it's just the water supply there. Could it be a very gentle water hammer?

Thanks

 

[CBW]

Could it be a very gentle water hammer

I wouldn’t have thought so, as you said it’s once every 30 seconds.

 

[Robert Thorpe]

Stops after a several minutes

 

[Harry Bloomfield]

Unless cold pipes can actually make noise like this from contraction?

They certainly can....

In our hall, we have CH pipes boxed in, in two corners. For years I would hear dripping type noises coming from their direction, for minutes at a time. I eventually traced the noise not to a drip, but to pipes gently expanding as the boiler came on and hot water circulated through the pipes. The noise is not so obvious now, since I upgraded the boiler and its controls - there is no sudden influx of hot water in the pipes.

I suspect your issue might just be cold water from underground cooling shrinking the pipe, which then gradually warms and expands as it takes up room temperature. Pipe rubbing against something.

If have lead pipes leading into your property, your local authority may have a duty to replace them free of charge to you.

 

[Robert Thorpe]

Thank you, I think you might be right, the ground floor is solid, no cellar and I can't see any damp anywhere. When radiators are adjusting to heat I don't mind that sound but this is somewhat trying, it's like the sound of water dripping onto a sideboard in the room. Hopefully I'll grow to ignore it.

 

[MJN]

You might find that in the summer, with its different ambient air and water temperatures, you don't get (or it being at least noticeably different) in which case it'd add confidence to it being an expansion/contraction (non-)issue.

 

[Robert Thorpe]

Is it possible for a weakness in the pipe to contract when new cold water from underground runs through it and then expand back to room temperature after several minutes and seal tight again, or still drip?

 

[MJN]

Follow the principle of Occam's Razor: the hypothesis that makes the least number of assumptions is most likely to be correct.