water boiling on 1999 BMW 323i

I have a bmw that has just had new water pump, pulley and tensioners fitted, I am now losing fluid under the car and the water level keeps needing topped up, its not overheating but last night after small run the water was boiling and the rubber pipes were scalding, it very sluggish when accelerating could this be cylinder head failure and if so are there any easy tell tale signs as I am mechanically challenged, thanks.

Asked by for the 1999 BMW 323i
could be a faulty water pump or instillation error.