So far I have tried ... 1) A replacement tap (now a Franke mixer)same problem although it didn't do it immediatley. 2) Moving the HW supplied to the 3.5bar Monsoon pump
So I am now at a loss .. I'd have thought the overrun on the pump would keep the pressure in the pipe, but it seems not to be the case. the tap can be turned off for just a couple of minutes and when it is turned on again we get the same lag. I can only assume it's a sticky valve but then why has it happened to 2 different taps. Plumber is also confused as to what it might be.
Any advice/observations appreciated