We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Each radiator head in this system radios back to the relay unit that
controls the boiler. If any one radiator head calls for heat the boiler will
be active. If no radiator heads call for heat the boiler is off. There is no
separate room thermostat as this would be entirely without a purpose.

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new' regulations.
He does not say whether these are building regulations or Corgi regulations.
He says "safety" and that he cannot sign it off (presumably Corgi-wise)
unless it has a bypass. He is saying that in theory if every radiator valve
failed and shut off, then the bypass radiator, which would be uncontrolled,
would allow the passage of water for safety reasons. He also says it will
save gas. The problem to us is he is insisting it must be one radiator that
remains uncontrolled. This is anathema to me! An uncontrolled radiator
chugging away every time the system is on for any one or more other
radiators.

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely event
that all TRVs were closed or faulty. Is there another function of a bypass?
Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do not
have a radiator in a room with a system thermostat. Our system will only
fire the boiler if one or more stats calls for heat. I take this to mean it
is fully interlocked?

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory? If they ever do, does a system that would not call for heat in
the situation where all TRVs are -shut- require a bypass? Is it true to say
the bypass is a safety item or is it to protect the pump? Or in some way
supposed to save energy?

What should I read? Has anyone any references? Any input would be most
appreciated

Nick