Water pressure problem

muckles

Plumber installed an upstairs WC and washhand basin in my house about two years ago.This is on the same level as the water tank.Last year there was an almighty bang and water was pouring down the side of the house.Plumber came back reluctantly and said it was just a valve gone which he replaced.Now when I turn on the tap(uniblock mixer) The water starts with a burst then dies down to nothing.When I flush the toilet there is no water from the tap.Now and again there seems to be a bit of water running down the side of the house from the upstairs overflow.
Anybody got any ideas how to fix this problem?
Many thanks.

ormus

sounds like the wrong type of valve was fitted.
and or needs adjusting. the tank is overflowing.

gas4you

Sounds like a blockage in the supply between the tanks and the tap. Did he open the gate valves properly after finishing the work?

muckles

Thanks for the replies.Further explanation is that the plumber installed a small unit to heat water rather than use the hot water from the hot water tank down stairs.He said he also put a valve on the cold water supply (hand wheel type) to control the water coming in to the sink.I think he was using this valve to control the water pressure but this is not working as I explained.
Should this have been set up differently?
Any further advice appreciated