"Christian McArdle" wrote in message
. net...
"Components:

A filling point.
A pressure relief valve and discharge pipe.
An expansion vessel
A pressure gauge"

"Automatic air vent" should be one of these points.

There is no requirement for an automatic air vent on a sealed pressurised
primary circuit. Sure, they're very useful and labour saving, but many
systems do not have them installed.

I know few. if any, systems that do not require an auto air vent above the
boiler on the flow pipe. In days gone by when there was no system boilers
with integral pressure vessels and all components had to be external, an
auto air-vent on the flow over the boiler was mandatory by all
manufacturers. You didn't think, you just put one in.