In article ,
"Autolycus" writes:
Or getting rid of the wretched things completely and using
sensibly-positioned thermostats and motorised valves of a size and
design that you wouldn't mind having them visible. I have used Sauter
AXT111 actuators, but they're so far off being a mainstream product that
they're too expensive for many purposes - and difficult to find with
auxiliary switches.

Guess who's in the process of designing a heating system and wants it
fully zoned - 5 rooms - and adjustable to real, understood, temperature
values, and set without grovelling on the floor, trying to move a valve
between four-and-a-tiny-bit and four-and-a-tiny-bit-and-a-gnat's.

I suspect that maybe OTT.

I designed and installed central heating about 6 years ago.
I split into downstairs and upstairs zones with separate control.
I did accurate heatloss calculations for each room and sized the
rads appropriately. TRVs are fitted on all rads except in the two
rooms with thermostats, but I simply leave them fully open all
the time. With the radiators matching the heat loss from each
room, all rooms match each other temperature-wise, and when the
rooms with the stats are at the right temperature, so are all
the other rooms.

If I hadn't done accurate heat-loss calculations, then TRV's
would have been necessary to get desired temperatures, but with
proper heat-loss calcs and accurately sized rads, they aren't
doing anything. If I'd known how accurate my heat-loss calcs were,
I might not have bothered fitting the TRVs at the time. (However,
they or something equivalent are needed by Part L nowadays.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]