HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !

Regular readers may recall the saga of my heatpump system - which was
causing the CH header tank to regularly overflow. This was finally
sorted by bleeding trapped air out of the heat store.

Systems looks like a conventional CH boiler - except that the 'boiler'
is a heatpump, and the return from radiator and DHW circuits passes
through a 200 litre, heavily insulated copper 'heat-store' before it
goes back to the heatpump. When the heat pump switches off the system
circulates water from the store through the DHW / CH until it's cooled
sufficiently.

Anyway....

The whole thing's piped up in copper / pex - the circulating pump has a
little brass float-type auto air vent on the highest point of the
circuit - but the feed to the top of the heat store had no such vent.

The only way to bleed the air from the heat store was to slacken off the
compression fitting at the top of the store and wait while the air finds
its way out - necessitates leaning over the store and applying lateral
pressure to the pex pipe to slightly unseat the pipe - a slow and
uncomfortable process!

So - I bought another auto air vent and fitted it as close as possible
to the feed into the heat store - confidently expecting it to vent air
... automatically ....

Trouble is - it doesn't grr
It's still necessary to do the 'lean over the heat store for a hour at a
time to let the air out'....

So - what don;t I understand about using these auto air vents ?
It's fitted pretty much at the high point of the circuit - certainly on
a level with the union into the heat store. Fitted into a 3/4" x 3/4" x
female threaded 'tee' - with the air valve fitted vertical and into the
threaded part of the tee...

Any ideas please ??

TIA
Adrian