...and in that situation, if a central heating pump/zone valve/thermostat/programmer/rad valve/existing fitting on pipework failed or developed a fault and you were happy to pay for those repairs yourself, fair enough!
That is a non sequitur.
The question was not, will I guarantee existing materials for 5 years free of charge, but: what will give the customer better value for money: 3 years on the boiler or 2 years on a cleaned and treated rad/valve.
If we take the hundreds of thousands of posts on this forum as sufficient empirical evidence to generalise, we can draw two conclusions:
1. Not a single post of somebody complaining about leaking rad/valve of a system that was flushed, pressure tested, and treated with inhibitor.
2. Hundreds, if not thousands of posts about faults on boilers of less than 5 years old.
just because an installation "probably wont" have a problem doesnt mean theres not value in the cover.
Again, that was not the question. Anything can go wrong, even the best quality materials installed fully to spec. It is more along the lines of: is it worth £1000 p/a to take out building insurance on your home against earthquake damage in London, or would you be better of spending money on protection against identity theft? [/b]