i am not sure what the pressure is, but the flow can be very low - the supply from the main in the street feeds 5 terrace houses on my row.
The noise only lasts 30 seconds or so and stops - or cuts the boiler out as a result of error.
The boiler was there when i moved in - however i assume...
i moved into a property with a Ravenheat 120T combi boiler. It makes a banging noise when the mains water pressure is low and the hot water tap is turned on. This lasts for about 30 seconds and then stops or brings an error warning up on the boiler.
I don't know why but this doesn't happen...