banging pipes

[optomist]

I have spent hundreds of pounds with plumbers recently and don't want to spend more unless I am 100% sure of a cure for my banging pipes. The last visit seemed to do the job but since the CH is on now most of the time the problem has returned with a vengeance. The noise isn't constant but makes me jump several times a day. If a drain-off (correct term escapes me for the moment) is required, is it something that an old lady could manage???...

Any advice greatfully accepted.

[Barquentine]

It's called water hammer. Something to do with an airlock somewhere in the pipes. I think you just turn off the water at the stopcock, turn all the taps on to empty the pipes, then turn the stop cock back on slowly to let the pipes fill up, but I'm not sure how that untraps the air. Try searching 'water hammer' on YouTube - lots of videos there will explain what to do.

[optomist]

Thanks Bar.. will try that, but will look up how to first..

[buildersmate]

Water hammer is to do with vibrations being set up in the pipework. It generally occurs in the cold water system when one particualr tap is turned on.

If you are saying that this banging only occurs whilst your CH is on, it is most unlikely to be water hammer. It is caused when the hot water flows through copper pipes that are mounted through notches cut in joists. When the system goes on (and the water in the pipe heats) it also heats the copper pipe which expands slightly, the expansion results in movement of the pipes in relation to the fixed joists through which they are mounted and the lateral movement causes a slight bang or scraping. The fault is in the way the pipes have been mounted - if they are too tight in the notches they can't move freely. The reverse happens as the system cools (although the heat up is generally the worst as heating occurs quickly whilst cooling occurs slowly).

If this sounds like a description of the problem you've got, it is somwhat surprising that a plumber can't tell you that.

Putting it right is fiendishly difficult and potentially expensive; floorboards have to be lifted and notches widened a fraction, or felt strips put below the pipes to slide on.

You may have to live with it.

[The Builder]

Yes water hammer is a mains pressure issue, this a heating problem.

If it's not as BM has suggested............

Violent banging is quite often in the "heat leak" radiator (there should be one in the system ... the one with no thermostatic valve on it).
Often the result of the pump speed being too high, possibly on a badly balanced system.

Sorry about the jargon, Optomist. The upshot is that you don't need a plumber. You need a proper specialist boiler guy. Preferably one with plenty of experience of your make of boiler.