Our pipes are knocking all through the house when the taps are turned off. Even when the toilets are flushed and finish refilling. We have very high water pressure. Will we need to call a plumber or is there something we could do beforehand.?
Welcome to the Bunnings Workshop community @Janinemc. It's terrific that you've joined us, and many thanks for your question.
Water hammer is caused when a pressure surge or wave of water is suddenly halted by shutting off a valve. It might be directly related to your high water pressure, but water hammer can be caused by the lack of air in your copper pipes. Air is compressible and acts as a shock absorber within the system. When the air leaks out, and only water is present, it slams into your valves when you shut them off and creates the knocking or water hammer.
In older houses, vertical sections of pipe were added to the system to act purely as air chambers. If it is an older house, I'd suggest you try purging the excess water from your lines and adding air to them. Turn your mains water off and then flush the toilet and open all taps in the house to drain the water. Once this has been done, wait 30 minutes before turning all the taps off again. Turn your mains supply on slowly, so it fills your pipes.
If this doesn't have any effect, you'll likely need to employ a plumber's services to install a pressure reducer or water hammer arrestor. A water hammer arrestor is simply a cylinder that holds air and acts as a shock-absorbing piston.