#2 & #3 thank you so much for your advice. Am currently waiting on a call back from BG, so will see what they have to say. Boiler was mended and serviced in October last year - I can't imagine that it has corroded since then. The heat exchanger hasn't been replaced as yet, it was when the repair man came to fit it that he mentioned the corrosion. The corrosion is not on the heat exchanger but the metal casing for the boiler and the plate/arm at the side that holds the heat exchanger in place. Just seems odd that a piece of metal plate inside the boiler (that you could see as soon as you remove the outer cover) can be rusted away so that a bit about 5cm x 4cm is completely missing and no-one mentioned it. If you have any more information that would be great, or if you would like to see the photos of the boiler they are on flickr, I can't post the link here, but you are welcome to PM me for the link. Thanks again for your replies.

My 8 year-old boiler was condemned 2 weeks ago due to corrosion. The BG engineer says that the corrosion at the rear of the boiler means the unit is no longer sealed/safe for use. We have had British Gas HomeCare 200 since before our Potterton Suprima 60 was installed, BG have been servicing it and taking care of it since then. We have had 8 breakdown calls since it was new as well as annual services. At no point have we been advised of any corrosion. The corrosion has clearly been going on for years (I have photos if it helps) – and I believe that BG should have spotted it and dealt with it within the 7 year time frame. The boiler was leaking water so we called out BG, they came and diagnosed a problem with the heat exchanger. New one ordered, then engineer came to fit it. He condemned boiler as there was a huge amount of corrosion at the rear of the boiler where the water pipe attached. He told me that this couldn’t be seen until the heat exchanger was removed. Now we have no boiler and apparently no leg to stand on. If the boiler was less than 7 years-old they would have to replace it under the terms of the policy. There is a second area of corrosion also on the heat exchanger – at the front. Incredibly visible once the outer cover is removed. Not just a bit of rust, but the metal has been eaten away to the point where the hole to attach the heat exchanger is not secure. I have phoned and emailed but at this stage, no joy – last I was told it was ‘just one of those things’ and basically it is my tough luck that I am without heat and water and that I now need to purchase a new boiler... ANY advice or help will be so gratefully appreciated, it is very cold here!