"Christian McArdle" wrote in message
et...
Am I missing something in my thinking, before I order the parts?

1. You may need something to prevent gravity circulation in the CH
circuit.
This will depend on circumstances, but could be either a 2 port valve or a
one way valve (with circuit flow set to be against natural convection). It
may not be necessary.

Why would you need something in the circuit to prevent gravity circulation
in the CH circuit, if control is added to the HW circuit. I presume that at
the moment, when HW only is running there is already no circulation in the
system? The current system will already be HW only or HW & CH. With a 2
port valve you get the options of HW Only / CH Only / HW & CH

2. Remove the TRV from the roomstat room. Some well meaning person WILL
turn
it down.

Agreed - but would work in the short term. Some TRV can be locked off to
prevent them turning.