In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:

My mother had her central eating boiler replaced a couple of months
ago, and I went up to see her for the first time last week (I know, I
know, but I do phone her every week). I was amazed at what has been
installed.

The original system dated from the 1970s, with no room thermostats.
TRVs were added later to all radiators. The new boiler has been
installed, but there is no by-pass circuit, much less a valve or flow
switch, so one radiator must be left on permanently. The only
effective control over heat is the boiler thermostat. I don't know
whether the system had a by-pass circuit before. Could there have
been a flow switch in the old boiler?

Putting aside the question of complying with the Building Regulations
(which it doesn't), how dangerous is it to have a heating circuit
entirely controlled by TRVs with no by-pass? I tried closing all the
TRVs, but the boiler continued firing and I could hear the pump
beginning to strain. What would happen if i had let this continue, or
my mother (who's nearly 80, and a bit forgetful) decides to lower the
only open TRV?

I don't think it will actually explode - but it's extremely bad practice.
The worst that will happen is that the boiler will overheat, its overheat
stat will trip, and your mother will have no heating. The pump will also get
a bit frenzied - but may be able to run in a stalled condition without
coming to any actual harm.

Does the boiler also heat the hot water? Is this the same system which you
mentioned in your earlier thread about not having a room stat?

--
Cheers,
Set Square
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