In an earlier contribution to this discussion,
Edward W. Thompson wrote:

The house of a friend is fully centrally heated but none of the
radiators are fitted with thermostatic control valves. The system was
fitted about 15 years ago, possibly longer.

The house has three bedrooms and a bathroom upstairs and the
downstairs comprises a hallway, large lounge, dining room and kitchen.
All spaces are fitted with radiators including the hallway. The
system is controlled by a simple thermostat in the lounge. Hot water
is by an indirect cylinder.

I was thinking the most appropriate plan is to install TRVs to all the
radiators except those in the lounge, where the thermostat is sited,
and to change the thermostat to a programmable type.

I will appreciate guidance whether this plan is sensible or whether
all radiators should be fitted with TRVs.

You don't say whether the system is fully pumped, or whether it is gravity
hot water and pumped central heating. If gravity, you should either convert
it to fully pumped or - at least - fit a zone valve and tank stat in the HW
circuit in order to provide independent control of HW and CH as well as
providing a boiler interlock. [Come back if this needs more explanation].

Fitting TRVs to all but one radiator is entirely reasonable. The rad nearest
the room stat should have two lockshield valves (and no TRV) so that it
can't be turned off without using tools.

Assuming it's a vented system, you *could* have a problem with pumping over
when most of the TRVs are closed, depending on how the fill and vent pipes
are connected. If this *is* a problem, it will need to be addressed. You
could also consider swapping the pump for one with automatically variable
output - such as a Grundfos Alpha - which will reduce the noise when most of
the TRVs are closed.
--
Cheers,
Set Square
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