I can't find that in my slightly older (2000) building regs tho.

The requirement is new from the 2002 building regulations. I suspect you are
simply still thinking in terms of pre-2002 requirements.

How about page 16, paragraph 1.41
"b) Where it is proposed to effect control by
thermostatic radiator valves, a room thermostat
(or other device such as a flow switch) should
also be provided to switch off the boiler when
there is no demand for heating or hot water."


Well every boiler I have ever seen comes with a thermostatic switch to
do just that.

No, the thermostatic switch is not enough. It must totally turn off and not
keep the primary circulating water hot. As every single gas/oil boiler in
existence has such a thermostatic device (or similar analogue modulating
control), why do you think they would mention room thermostats or flow
switches as interlock devices?

If the system you propose is installed, the boiler will operate (to heat
primary circulating water) even when all TRVs are closed and the hot water
cylinder is hot. This is not allowed. I'm afraid you appear to be in a
minority of one in insisting that an all TRV system is allowed without room
thermostat or flow switch.

Yes, but it doesn't say you have to set up a system of two suites of
thermostats essentially fighting each other.

Indeed. There are three methods proposed.

a) Install TRVs and a roomstat. You can balance and design the system such
that the TRV rooms heat up marginally quicker than the room thermostat
rooms. This ensures that the TRVs turn off before the room thermostat
engages the boiler interlock. This provides good temperature control in all
rooms.

b) Install a flow switch that determines that when no flow occurs through
the TRVs, the boiler is turned off, and the circulating water cools down.
This provides even better temperature control in all rooms.

c) Install a fully controlled zoned system (i.e. room thermostat/no TRV in
every room).

Christian.