Auto Air Vents for hot water system

[luckey]

can anyone tell me what type of auto air vent is needed for my hot water system i have been told by a system engineer that i need an auto air vent as now i have to keep bleeding the valve to get hot water, he also metioned the system may need close coupling. is there different pressure types on valves that i may need and temperature requirements?

[buildersmate]

I feel you've only been given half a story. What systems engineer would tell you you need a auto air vent without suggesting what type?
Now the answer will have to get technical. Do you know if your system is vented or unvented (pressurised)?
If it is unvented, an auto air vent is normally fitted as standard. And if you are getting lots of 'air' in an unvented system, it is because there isn't enough corrosion inhibitor in the primary water circuit and the water is slowly eating away at the inside of your rads. One of the byproducts of this is gas - hydrogen gas - and this 'air' you refer to is this in fact gas. It is true that an auto air vent will remove this gas but you are treating the symptom, not the root cause.
If your system is vented (and hence has a small reservoir tank in the loft) it IS just possible that the air is getting in through contact with the reservoir tank (through bad design, usually), but it is much more likley that it is created again through lack of inhibitor. I suggest you check this first - rather than get involved in the need or not for an auto air vent.

[luckey]

i have been told that my radiators need flushing or draining at some point as sometimes it takes a while for the bottom room radiators (2) to heat up, as for the auto valve theres a pipe that joins part of my hot water tank in airing cupboard and at the top of it theres a screw which i turn to let air out manually as its not auto, and sometimes when my hot water isnt as hot as it usually is then i turn this screw and air comes out then within half an hour my hot water is as normal, problem is it is doing this every week to fortnight now was told by the engineer that i need an auto air vent fitted where the screw is, does this help at all?