Would this be your recommendation against a Vaillant, which is my other option (plumber is agent for both)? Thank you for the link above, which I'm sure is a very good analysis of condensing boilers and their requirements, but unfortunately dementia set in about half-way through. I frequently see plumes of white whatever shooting out from neighbours' flues; esp. after turning on, I think, and wondered what this was, as my ancient Potterton doesn't do that; in fact, there's rarely anything much to see, even in frosty conditions.
How does one ensure that the return temp. of the water (htg. or just water or both?) is at that efficient condensing level, esp., as with Steve G above, unused rooms are either on tick-over and bedrooms are off during the day (with doors closed, of course)?
As I'm awaiting a quote for a refurb. (boiler, cylinder + a couple of TRVs etc.), I'd very much like to get this installation right as well as operate it as efficiently afterwards as poss. (vented system here). I gather that anything will be massively better that my eighties boiler but I'm a little sceptical, though the whole system is underpowered and clogged up after it was last emptied, but not flushed, 12+ years ago.