I'd probably change it, in all honesty.
When you come to sell the house, the buyer will undoubtedly use the old boiler as a negotiating tool to lower your price. Typically they get a boiler man to give them a hefty quote and set this against your asking price.
Also you will get a poor HIPs rating, so all in all, I'd change it for a modern unit. If you want it to last, get a 200 series Viessmann - their top end 300 series was recently dropped by Viessmann UK because they thought there was no market for it. Or if you are very wealthy and have a separate boiler room, get a Kidd. It exceeds the build quality of the kingfisher, was designed around the same time but was/is massively more efficient.
Alternatively, look out for a scrapped kingfisher and swap it out. But this option could fail tomorrow, has no warranty, and is iffey from a building regs perspective.