No open vent boilers were best buys but the top of list was the
Vaillant and at the bottom was the Potterton promax

From the online version they appear to have made no comment on or
allowance for (i) the effect of the return temperature on efficiency or
(ii) the cost of upgrading radiators in order to make it practicable to
reduce the return temperature. Is it naughty of them to show potential
savings on heating bills based on 90% efficiency and costs for boilers
alone?

For me (with 20+ year old albeit unvented system and separate multipoint
water heater) in a small Victorian terrace with suspended floors the
need to upgrade radiators in order to get anywhere near 90% has been a
big factor in doing nowt. Or (as is increasingly likely) have I
misunderstood what wd be involved?

--
Robin