I recently acquired a Stuart 501 Boiler. It still had the asbestos boards on the inside of the side plates. This has been safely disposed of. Can anyone suggest a replacement material, and where to get it please?
You could pop into a good builders merchants or roofing suppliers and by an "undercloaks board". These a fibre cement boards about 4ft long and 6" wide so enough for your boiler, cost about a quid each
Kaowool is OK if it is supported. If it needs to be self-supporting try a Skamolex (vermiculite) board, OK up to red heat – you can cut it into thinner sheets with a saw (use some sort of guide).