As a general system question, when using TRVs, is it normal to *not*
have any room thermostats at all and what is the best practice for
managing this?

It is permitted to use TRVs on all radiators and with no room thermostat.
However, you must still achieve boiler interlock if you wish to comply with
the Part L1 approved document.

One way of doing this is the following:

1. Install automatic bypass valve.

2. Install flow switch in heating circuit (*AFTER* ABV, *BEFORE* radiators)

3. Use flow switch output as a call for heat (simple on S-Plan, more complex
wiring for Y-Plan)

4. Wire pump permanently (or for a more sophisticated system, run the pump
on an 'OR'ed combination of the boiler pump output and a timer which
produces 5 second pulses every 10-15 minutes when the programmer CH On is
active).

Should I have all of my rads with TRVs or just leave one without?

Either. TRVs on all radiators is preferred. You can use a permanently open
radiator (lockshield both ends) instead of an automatic bypass valve, but it
must still be the only radiator BEFORE the flow switch. Putting it after the
flow switch will result in the interlock being ineffective. Putting any
other radiator before the flow switch will result in that radiator's call
for heat being ignored (although it will still heat up if other radiators do
call for heat).

Christian.

P.S.

You should still subzone the conservatory if at all possible, as this would
allow different timings to the rest of the house. It is possible, if you
want reduced timing periods for the conservatory but don't want the
disruption of running new zoned pipework, to do a "subzone lite". To do
this:

1. Implement the flow switch interlock above.
2. Do not install TRV in conservatory.
3. Install 2 port 22mm zone valve on conservatory radiator/convector.
4. Install programmable room stat in conservatory.
5. Wire zone valve to run when room stat activates.
6. Ignore zone valve switch outputs.

This will result in the conservatory system operating as a separate zone,
provided that the house programmer is set to heating on. This is a very good
idea, as it allows the conservatory to be heated only when required. If you
use it as a dining room, for example, you can set it to come on from 7pm to
9pm, for example, whilst being cold the rest of the day.