On Thursday, 24 October 2019 21:22:18 UTC+1, alan_m wrote:
A few years back whilst I had the central heating system drained down I
fitted auto bleed valves to my radiators (Aladin Autovent)

https://www.amazon.co.uk/Aladdin-Aut.../dp/B01L4P1IO6

They worked for a while.

I recently drained down the system again to remove radiators for a few
weeks to facilitate some building work. I have now re-instated the
radiators and have found that zero (out of six) auto bleed valves are
still working. This includes those on 4 radiators that have been
sitting around, fully drained for a few weeks.

Luckily I still had the manual bleed valves on the other side of the
radiator which I've used to remove the air from the system. Even with
the radiators on and running at full heat for very many hours a second
check of the radiators resulted in some air having to be removed showing
the auto bleed valves were still not working.

As a result I cannot recommend the use of the Aladin Autovent valves but
has anyone had any experience of auto bleed valves fitted to radiators
that work long term?

I do not anticipate any problem now with air entering my system until I
again drain down or remove/replace a radiator.

I do have some auto bleed valves fitted to the pipework high points that
are still working after 20+ years. These values are not suitable for
radiators and are of the type
https://www.screwfix.com/p/bottle-air-vent-15mm/34359

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

There are two sorts.
One has a float.
The other has a material which shrinks when it dries out (usually a washer) and swells when wet. You have to soak them in water (or let them be soaked) before they close off.
Haven't seen the latter for years though.