We have a Glow worm boiler with a pressurised water tank system. We have no hot water - the boiler is 14 years old but has been serviced every year an dis still woking. The plumber has told us we need to replace a part of the hot water tank that adds cold water to the hot as it comes out of tank?? We replaced another pump on the tank about 3 weeks ago for £170 this time he is asking for £180 - should we do it or replce the whole system for a combi boiler - we have a 3 bed detatched house with 3 kids, ensuite and family bathroom??