We have a Alpha 240 Eco combi boiler. Everything was working fine until i decided to try the central heating before things got to cold. All the radiators heated up (although some a bit hotter than others) and i thought we would be set. However, after switching the central heating off i found later that night that the hot water was starting to play up. Basically, i turn on the hot water, the boiler fires up, makes a howling noise for about 2-3 seconds and hot water comes out of the taps. After a very short time the boiler then shuts down. A little while later the boiler fires up again, before once again turning itself off (repeat for as long as you run the water). The result is a luke warm bowl of water or very miserable shower. The central heating however, remains absolutely fine. I called British Gas who said that the heat exchanger was getting blocked. The engineer recomended fitting a MagnaClean device and changing the heat exchanger, quoting £260. He did make a show of taking the heat exchanger off and showing my wife the black particles (no jokes please) but i am concerned that we might be being had over. A friend had a similar experience with British gas and there eagerness to sell heat exchangers. Any advice on the price quoted and the work proposed would be appreciated.