Plumbing: loud vibrating when using cold tap

TheCyclingProgrammer

In the last week or so we've been having an issue with our plumbing. If I open the cold tap in the kitchen (which has the highest pressure in the house) too quickly there's a really loud vibrating noise coming from the bathroom above. This also happens when the washing machine is running and to a lesser (but still noticeable) extent if I open the cold tap for the bathroom basin.

The vibration goes away if I close the tap slightly and doesn't come back if I then open the tap fully again (slowly).

The loud vibration noise seems to be coming from within the boiler but I suspect this is a symptom and not where the vibrating originates - if I isolate the cold feed to the boiler while it's happening the noise from the boiler stops but I can still hear and feel the vibration on the cold water pipes.

Another possible clue is that I can also feel the vibrations if I touch the top of the cold bath tap (I can't feel it on any other taps, or the pipework below the kitchen sink or bathroom basin). If I open the bath cold tap just a small amount the noise stops. I'm guessing this might be because it's easing the water pressure on that section of pipework.

Based on all the above I think the source of the vibration is somewhere on the cold water pipe between the bath and the pipework below the boiler.

Any suggestions on the cause? Could it be something as simple as a pipe becoming loose? It doesn't sound like the pipe is rattling, it feels more like its pulsating/vibrating, if that makes sense. Unfortunately the side of the bath is tiled so I'm concerned we will need to open this up to fix this. It's strange that it has only just started happening.

dggar

Have you investigated the main stopcock to the house. You could try closing it by half a turn to a turn and see if that makes any difference.

Apodemus

As mentioned above reducing the pressure might help. If this has just started it may be because that with the holiday season, there are fewer of your neighbours at home and you are getting the full pressure from the pipes. I'd hold off on any fancy solutions until after the summer hols are past, just to see if the problem goes away.

ariba10

The pipe work is not adiquitly secured.

(Your pipes need more pipe clips)

Moss5

Both suggestions are valid. Inadequate pipe fixing and tap washers can cause water hammer. Do not ignore. It can cause pipe fracture.

http://www.wickes.co.uk/Sioux-Chief-Water-Hammer-Arrester-1-2in/p/143498

http://www.screwfix.com/p/thomas-dudley-ltd-dw660-h-water-hammer-arrestor-bsp-connection/9813r

http://www.screwfix.com/p/prv-with-gauge-15-22mm/41943

TheCyclingProgrammer

I don't think it's water hammer - as I understand it water hammer is caused by the sudden stopping of water, not turning it on.

I have tried partially shutting the stop valve but that didn't seem to make much difference.

An insecure pipe seems like a good possibility though I'm not her why a pipe that's probably been there for years would suddenly come loose. We can't access the pipework under the bathroom floor as it's tiled.

TheCyclingProgrammer

Just tried it again and it no longer seems to be doing it. It could be coincidence but the bath is currently half full for my children's bath time. I will try it again once the bath is empty to see if it starts again (I'm not sure how the bath having water in could make a difference).

Moss5

Do you have a hot tank somewhere and a cold tank in the roof?
If you run a bath, it takes some time to replenish the cold tank.
During this time, the dynamic cold-supply pressure will fall.

TheCyclingProgrammer

No tanks, just a combi boiler. All cold water taps are direct from mains.

Bath is now empty and it's still not making the noise. Will try again tomorrow.

TheCyclingProgrammer

Ok it has started doing it again. This time after flushing the downstairs toilet.

This could be a coincidence but it does seem to have started since I cleaned the parts of our concealed Grohe toilet cistern. We were having problems with it continuing to let water run into the bowl after the flush had finished. I was advised by Grohe that I need to take out and clean the flush valve, which I did. It hasn't fixed the problem so I will need to go back to them. I'm not sure what, but could I have done something while doing this that has created this problem?

TheCyclingProgrammer

Well I'm pleased to say I think I've traced and fixed the problem and saved myself a plumber call out. I partly have my wife to thank for pointing out this started after I "fixed" the toilet.

After opening the taps to trigger the water hammer (I now know that water hammer can also be caused by other things besides sudden shutoff - apologies to Moss5) I was able to stop it immediately by turning off the cisterns internal isolation valve.

I then realised that when e water hammer occurred, the toilet was starting to let water into the bowl again - this time the culprit wasn't the flush valve (which I think was the issue before) but simply overflow as the inlet valve was starting to fill the cistern too high. Another clue!

I removed the inlet valve and discovered that having cleaned the various parts as shown in the manual, water had become trapped behind the diaphragm. Emptied it out, dried it off, refitted and hey presto, no more water hammer (touch wood).

So if I'm understanding what was happening here, the water in the diaphragm was causing it to start pulsating open and shut and causing the pulsating back along the pipework. I think. Am I right?