Banging pipes when boiler not on

[Big_les]

Hi guys,

Hoping someone can advise on this slightly unusual problem. We have a combi boiler downstairs (Semia Condens). If I run the hot water OR the heating for any length of time, what appears to be the pipes in the bedroom floors upstairs (both rooms) emit a really loud thump sound every few minutes, like someone has hit the pipe with a mallet. It does it on heat up and cooldown alongside the more usual tap tap tap sounds, but what's really weird is that even hours later we will hear this loud thunk occasionally until finally it stops. The only way to avoid being kept awake is to make sure the boiler is off well before we go to bed, and ideally that we don't use hot water (though we can get away with small amounts).

For this to happen without the boiler being on, I presume it must be down to thermal expansion/contraction. But it would be good to get some educated views before I start pulling up floorboards to stick padding under the pipes, though I do realise I may well need to get a plumber in.

Thanks

 

[Last Plumber]

Yes, it sounds like expanding and contracting pipes. Trouble is, sound travels well through piping so pinpointing the area is not easy.
You can only really start where you think it is loudest and look. It may be really obvious, I hope it is. Good luck.

 

[Big_les]

Yes, it sounds like expanding and contracting pipes. Trouble is, sound travels well through piping so pinpointing the area is not easy.
You can only really start where you think it is loudest and look. It may be really obvious, I hope it is. Good luck.

Thanks for the reply, very much appreciated. Do you think it's worth going straight to a plumber to diagnose and fix this? If it will save time and hassle I would do that. But if he is likely to spend just as long trying to isolate and solve the problem, then obviously I'd rather take a stab than throw money down the drain.

Thanks again in any case.

 

[Last Plumber]

Personally, I think you're best getting someone to hear it and confirm it. It is very difficult diagnosing things on a forum going off people's descriptions. I'm sure you understand what I mean by that, I have no doubt you've described it well and it does sound like pipes. However, it could be something a plumber would recognise as something else if they heard it for themselves.

 

[Big_les]

Well, I've had a look and fortunately someone had already hacked up a couple of boards to install some wiring, so I was able to get a look at the main two copper pipes coming up from the boiler and across the floor. I had to lower my phone into the space to see under the intact boards, but right away spotted one of the pipes taking a 90 degree bend and going UNDER the joist at a slight angle. I suspect this is the cause of at least some of the racket. If so, it will be a lot harder to access and to get a clip or padding between the pipe and the joist. If I can get the board above up, I can at least experiment with pushing something between the two to see if it reduces the noise.

 

[ShaunCorbs]

can you get your hand on it if so get the turn the boiler on and make it start making the noise and put your hand on the pipes you should be able to feel which one is having the issue/ making a noise

hope this makes sense

 

[Big_les]

It does, thanks. I've managed to narrow it down to one pipe by doing that, and have (with ear to the boards) traced it into the other bedroom, or possibly where the pipes pass through the dividing wall. Next attempt will be to pull up a board or two in the other room.

Worst case, I've narrowed it right down for a plumber to sort. Thanks for your help both.

 

[ShaunCorbs]

It does, thanks. I've managed to narrow it down to one pipe by doing that, and have (with ear to the boards) traced it into the other bedroom, or possibly where the pipes pass through the dividing wall. Next attempt will be to pull up a board or two in the other room.

Worst case, I've narrowed it right down for a plumber to sort. Thanks for your help both.

and done most of the hard work lifting flooring and boards etc