I have read as many FAQs, previous threads etc as i can find, and learnt
quite a lot, but would still appreciate advice if anyone can spare it.

I live in a 100 year old semi-d house, with existing conventional
floor-mounted boiler (approx 18 years old), open vented central heating
with a mixture of radiator types, hot water from cylinder, and a pumped
shower. I intend to get rid of most of it, and install a new condensing
combi boiler in the cellar, convert the central heating to a sealed
system (keeping about half the radiators, replacing / relocating the
rest), and convert the hot water to mains pressure (get rid of the
shower pump and cylinder etc). There's one bath, one shower and one
kitchen sink, with only one likely to be in use at any given time.

The work will be done by an installer (so this isn't really d-i-y) but
I'm planning to specify a Worcester Greenstar 35CDi combi boiler,
Honeywell CM67 programmable digistat (probably the wireless one, so that
I can experiment with locations), Myson (round-top) rads to match the
retained ones already installed, ? TRVs. I've calculated the required
radiator sizes using an old copy of Myson Heatloss Manager (Myson don't
seem to have this on their website any more, which is a shame).

I would be grateful for any reassurance that this all sounds reasonably
sensible, but in particular:
1) With condensing boilers is it still important to get the 'right' size
or might there be benefit in over-sizing a little?
2) Any problems using a Honeywell digistat with a worcester boiler?
There seem to be other similar products (eg Danfoss) - are there
significant differences? Surpisingly the manufacturer's websites don't
seem to give clear details. What we need is 7-day control, with the
ability to over-ride for periods, both for days (holiday) and hours
(during the day), without having to re-programme.
3) Controls generally... I've seen a number of threads about the wisdom
or otherwise of a traditional room thermostat in the hall, no TRV on the
radiator etc. (I think) I understand the requirement to achieve 'boiler
interlock' by one means or other. However I wondered if anyone has
knowledge or experience of more 'hi-tech' solutions, eg Honeywell
CM-Zone? Also, any preferences for TRV manufacturer?

Sorry about the length of the post. Any comments would be much
appreciated.
--
Rick Bowlby

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