I moved into a new house in 2000 which had a pair of Keston C170 boilers.
From the outset these proved hideously unreliable. However, it also became apparent that they had not been installed correctly in that the 'manifold' approach recommended by Keston had simply been ignored. I finally paid to have the two boilers replumbed into a manifold and the result has been a huge improvement in reliability - but problems do still occur.
I have not kept a log of the faults and failures I have experienced since 2000 but I'm certain, on average, that I've had to call out an engineer at least once a quarter throughout the period.
Just about every component that could fail has failed at some point on one or other of the two boilers including two heat exchangers, one fan and several RAM CPUs. The cost has been HORRENDOUS.
On the plus side, when they are working, the C170 boilers are great - very efficient and seemingly economical. Although the Services Consultant who designed the house's heating system reckoned two boilers were needed, we've only ever run one to heat a 7500 sq ft house and pool - which is just as well as it leaves the second boiler in reserve to take over when the first one fails, as it inevitably will.
Given the choice, I wouldn't want Keston to heat my next home - and especially as during my first 30 years of home ownership I only ever had Potterton and their boilers never let me down even once.
You have been warned!
PS Message to Keston: Try a lot harder; do a lot bettter; or jack it in and let those who know how to manufacture a quality product get on with the job without you.