"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Christian McArdle wrote:

[So what happens if you have gravity primary circulation in the HW
circuit (with no zone valve and tank stat to convert them to C-Plan
systems) - as a great number of systems still do?]

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

Christian.

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

illegal on new systems.