Hello, I have been having water hammer after flushing toilet in the past couple of weeks. I have tried turning off the stopcock and opened all taps to drain all the water in pipes and toilet then turned the stopcock back on for 2 to 3 cycles. The water hummer then fixed for a few flushes but it comes back. It's ok a few weeks ago before we fixed the bath tap which required to turn the stopcock off and back on. Or is it the problems with the push button flush unit needs replacing as it's 4 years old. Thanks.