"IMM" wrote in message
...

AFAIK the CM67 can operate a 230v modulated valve. If that is not the
case
(specs vague on this from wjat I have seen), then I think the Landis &
Staefa version can. If so, I would go for this controller not the CM67.
I
tend to prefer Landis & Staefa controls anyhow. They are much more
reliable, better made, better user intefaces and generally cheaper too.

The Landis & Staefa RVP will give proportional control by driving a servo on
top of a mixing valve, measuring the flow, return, inside and outside
temperatures, deriving the setting from a pre learnt heating curve for your
house. Assuming your boiler already has a RVP the extra cost is about 200
quid for the valve and servo. With a rad based system I would recommend
fitting this type of control as the temperature swings are eliminated by
matching the heat input to the heat loss. But with UFH time constant you
would really gain much from these controls.