I am also getting quotes to replace our v old boiler.
Decided to get a British Gas quote first so as the rest can only be better.
I'm looking at changing the HW cylinder to be mains pressure as well which I know will not be cheap so was expecting a high quote – but a Vaillant system boiler, tank, 3 new rads, scale filter, flush etc = £6.5k !! And that was with a 3rd off.
He reckons a combi would be 4k.
More quotes to come but after a year looking at options and talking to friends I'm going for a Vaillant.
The main problem I expect to find is finding a local chap/company whose quote is reasonable where I can trust him/them to do a proper job.
I feel sure that BG would do a top job but at one hell of a cost.