Cold water pipe knocking!!!

sid1234_2

A bit of help required from forumites,

I have a combi boiler system in my home and the boiler is working fine. I changed the bathroom toilet cistern last week and because of this, i had to turn the water off to the whole house via the tap under the kitchen sink.

The tap was very hard to turn but it did turn and the cistern was changed.

I now have knocking noises coming from my main cold feed pipes. It is loud enough to wake me up at night. It doesn't seem to happen when i turn on any taps in the home but happens intermittently when the central heating is on.

I have put the stopcock in the kitchen really low just incase there was too much pressure but this hasnt resolved the problem.

Does anyone know what could be causing this or how i should start investigating?

Le_Kirk

Open the stopcock fully, see if that cures it.

ariba10

If opening it fully doesn't cure it then try closing it half a turn at a time until
The noise stops.

sid1234_2

I could try doing that but because the noise is intermittent, i wont know if ive cured the problem straightaway.

Do you think changing the stoptap will help because it sounds like the above replies think that is the main source of the problem?

Marktheshark

Usually the stop tap, a good spray of WD40 might get it moving.

sid1234_2

Marktheshark wrote: »

Usually the stop tap, a good spray of WD40 might get it moving.

The stop tap is moving fine now but the knocking in the pipes is the major problem as I have no idea what it could be.

Le_Kirk

Pipe hammer is usually when pressure is applied or removed suddenly. In my house I can cause a particular pipe to knock if I turn off the downstairs toilet tap too quickly. I would look at the ball valve in the cold water tank, it could be sticking causing pressure to come and go quickly.

sid1234_2

It is a combi system so i dont have a cold water tank.

Le_Kirk

sid1234 wrote: »

It is a combi system so i dont have a cold water tank.

Ah, back to the drawing board then. I assume then, that all your cold water taps are mains pressure fed? When is your pipe knocking? If you have no taps (hot or cold) open and you have not just flushed the toilet (i.e. cistern filling) then there is no water flow and should be no hammer.

unclebulgaria

First thing is DO NOT use WD40 around potable water sources and that includes the rising main stop !!!!! It is not a true lubricant and will taint the water!! If you must use a lubricant use a silicone based grease from the plumbers merchants specifically for taps.
Go around your home and open each tap a bit at a time and see if you pinpoint one that's possibly causing the water hammer, it may be dripping slightly. If you pinpoint the tap it may need servicing. Failing that you can get arrestors fitted that will take up the change in pressure that's causing the hammering.