Hi Folks, water hammer occurs with all of the taps in my house, both toilets and the washing machine. I had a couple of arrestors fitted and the problem went away for a couple of hours so I guess something must have triggered it again. I recently switched off the stopcock and drained the remaining water from the pipes. On switching the stopcock back on I found that the noise had stopped; alas it started up a few hours later ( Any thoughts on how to track down the cause would be appreciated. I'm not quite sure why draining the water from the pipes 'fixes' it for a short period of time.