Can anyone advise where is a good place to buy secondary heat
exchanger for Britony Combi 80 boiler? In the past, I have usually
bought locally from the Plumb Centre, but price was high. (about £100,
IIRC). I'd like to buy one now, before the current one gets scaled
up. Mail order, perhaps... I live in a very hard water area and it
seems I have to replace the thing almost every year.

Many thanks

Ed S