hi, is this boiler very old?, poss causes..plate heat exchanger worn if old boiler, gas pressure low due to small pipe diameter,or blocked,or gas valve fault, i guess it may be time to change boiler if its over 10 years old.
peter, February 2011
Either the heating matrix is blocked with scale or the bath flow rate is more than the boiler can handle. Try slowing the flow of the tap down in slight increments until it starts getting hot. If it turms to a dribble before getting hot then it is most likely blocked.
