In an earlier contribution to this discussion,
IMM wrote:

All such systems and even fully pumped systems without cyldiner
thermostats are indeed dangerous.

Agreed, but there are lot of them about - as evidenced by many of
the questions in this NG!

illegal on new systems.

Yes - but on the basis of thermal efficiency rather than safety.

I believe safety was factored into their decision.

Do you know of any legislation which explicitly forbids gravity systems
running at boiler temperature? As far as I am aware, such systems would be
implicitly - but not explicitly - outlawed simply because they fail to meet
the boiler interlock requirement. My understanding is that boiler interlocks
are only required on fuel efficiency grounds.
--
Cheers,
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