Is pressure rising above 3 bar ? if so, you need a new flat plate-to-plate domestic hot water heat exchanger. Take a note of Make and model and Gas Council no (GC no). Go to heating spares shop, and they might have one in stock. If not they can order you one. My guess is that it will cost about £60 - £70. Then you need a fully EXPERIENCED Corgi registered engineer to fit this part for you. They will probably charge an hours work of about £60. Hope this of some help.
Curtis Lee Patrick, February 2008
