Recently the hot water tap in my kitchen had developed serious water hammer, a vibrating, thudding sound through the pipe once the water got hot.
And I couldn’t get the mix right in the shower either. A slight turn of the taps one way, and it was too cold, and a slight deviation the other way, too hot.
However, the gas lines were replaced last week, and I had to re-start the gas hot water manually.
After doing that, I discovered that both problems had vanished.
So if you’re having difficulties, try adjusting the temperature at the hot water service before messing around with washers or any other work.