Asbestos in boilers...

Asbestos was commonly used in boilers until it was banned from use in boiler manufacture in 1984. 

Several pre-1984 boiler models are long-lived enough for examples still to be in use. The problem with these boilers is friable asbestos seals (on combustion camber covers for example). These seals are fragile and disintegrate when disturbed, shedding asbestos fibres into the atmosphere, presenting in my opinion a serious health risk to any technician working on that boiler.

I maintain a short but growing list of boilers that I know from experience contain such seals, and I decline to work on these due to asbestos health risk. These models are all at least 25 years old and I advise prompt replacement if you own one because keeping it maintained is likely to be ever more difficult as fewer and fewer gas technicians are to work on them

Here is my current list:

Potterton Kingfisher Mk1
Potterton Flamingo Mk1
Glow Worm Space Saver Mk 1
Ideal Concord
Ideal 'E' type