water hammer

Nov 20, 2004 4 Replies
R

A friend has a problem with water hammer, that she showed me today. It's the usual one-off "thump" when the tap is turned off.



The arrangement seems to be that there is no hot tank, the hot water being supplied on demand (and presumably at mains pressure) from a combi boiler. The system was installed as part of the central heating system about a year ago. There is an upstairs header tank in the loft which I assume feeds the cold supply to the bath, wash basin and toilet. I suspect there used to be a water tank with immersion heater before the new system was installed.



The water hammer occurs every time that the hot tap is turned off - bath, wash basin or downstairs sink. It doesn't occur at anytime the cold water is used. I don't think that it occurs when the cold tap is used in the kitchen. The kitchen taps go through a mixer and this is hard to turn off suddenly in one go. The bath and wash basin taps are mixer taps with a single lever that has a left/right movement for mixing and an up/down movement to turn the water on/off. This can cause the water to stop immediately.



Although this only seems to occur from the hot taps, I assume that it also occurs on the cold water main taps (I forgot to ask if it happened with the washing machine.



She called in a plumber who replaced the ball valve in the header tank, but that made no difference (I'm not sure why that was changed, given that the it happens from other sources, but I assume that the plumber knew what he was doing.



Any suggestions as to what could be done?



Thanks



Roger (my reader sometimes loses mail/newsgroup messages



- if you think you should have had a reply/comment, please e-mail me again. Ta!)


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B

Try holding on to the pipework where the noise seems to be coming from. This is usually under the kitchen sink for some reason, could be because this area is normally boxed in and no one gets a chance to fit pipe clips. You should feel the thump when the tap is turned off. If you can feel the thump, then the pipe needs a clip sited on the bend where it turns along the direction of the floor, or on the vertical section up to the tap itself. These rattles are common and clipping along the parts that reach the taps helps a lot. Good luck with it.

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J

If there are no obvious unsupported pipes floating about, then the quickest solution is to fit a shock arrester.

See part number 11355 here:

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B

In message , snipped-for-privacy@cix.compulink.co.uk writes

After something like four years in place our combi fed hot system has just started doing this when the hot's switched on.

Anyone suggest why it should have suddenly started happening?

I don't think he can have done if it's direct feed hot water and the thump only affects the hot.

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R

Thanks for the comments.

I have spoken to the friend again and apparently they've already been in touch with the gas people who installed the central heating etc and (I assume it was after a visit) they said it's nothing to do with them and suggest that they chase up the people who subsequently fitted a new bathroom suite in.

I don't know if those people are the same as the one that fitted a new ball c*ck in an effort to stop it.

I hope to be going round there on Saturday, so will try and get more information/check things out then.

Roger

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