No.  Aladdin Autovents do not leak.  They are guaranteed to operate for 3 years, and guaranteed leak-free for life.  They contain a patented mechanical valve that positively closes when water gets to the internal mechanism of the valve.   The Hygroseal™ range has a 5 year replacement guarantee.

 With a 1/2" BSP thread, the threaded hole in the tapping at the top of the radiator is approximately 20mm diameter – you should be able to fit your index finger in the tapping. The plug screwed in to the tapping will either be a chrome hexagonal valve, or a 'plug' with a square cavity in it. 

 Yes, on newly installed closed systems there will be a small pressure drop over the first 2 weeks or so as dissolved air separates from the fresh water (around 17% by volume) , but any further pressure drop would be due to loss of system water (leaks). Some installers are priming a newly installed system to about 10% more than its operating pressure to compensate on a system fitted with Autovents.

 Yes, on newly installed closed systems there will be a small pressure drop over the first 2 weeks or so as dissolved air separates from the fresh water (around 17% by volume) , but any further pressure drop would be due to loss of system water (leaks). Some installers are priming a newly installed system to about 10% more than its operating pressure to compensate on a system fitted with Autovents.

 5.  On a Closed system will fitting automatic vents cause the

    pressure to drop to zero and the boiler stop operating?

 The answer is linked to the above – continual venting will be due to new air entering the system (through micro-gaps in joints etc.).  Once the fresh water has vented its 17% of absorbed air the volume of water cannot further reduce in size – so if you still experience pressure drop it’s due to water loss, i.e. a leak, which will require to be cured.

 Yes.  Fitting the Autovent should reduce the need for corrosion inhibitors as all your radiators will be free of air, but we do recommend their use because corrosion leads to further gas collecting in the radiators.  To allow inhibitors to be used ensure at least one radiator still has a manual vent plug fitted at the opposite end to an Autovent, as this will allow the inhibitor to be injected.

 Leak-stop products can jam valves in certain circumstances.
We do not recommend their use.

 The first time radiators fitted with these Hygroscopic™ Autovents are filled the air hisses out until water hits the hygroscopic washers and then they seal (you will often see a small ‘bubble’ of water after the first fill).  If more air/gas builds up in the radiator, it will not escape until the hygroscopic washers have dried a little and have shrunk enough for gas/air to escape.  The time it takes for the hygroscopic washers to dry and shrink varies according to ambient temperature and humidity: see the table in the Technical Details on the Product Page.  So please, give this valve time to dry, before contacting us. 

 Yes. 

Cartridge version: by loosening the cartridge slowly until you can hear gas/air escaping.

 Yes, provided the temperature of the piping allows the valve to operate at 35°C for the Hygroseal vent.

 11. Can the valves work on negative pressure systems?

     On about 1 in 400 systems air may be drawn in to the

     system where either (a) there is a radiator close to the

     suction side of the pump or, (b) where a radiator is higher

     than the water tank, in which case when the pump stops

     running a vacuum forms (e.g. in loft conversions).

 If after a minimum of 5 years, the radiator starts getting cold at the top, the cartridge may require replacing in order to continue venting automatically.

 13. Air collecting in a radiator can be an early indication of a leak

     in the central heating system.  Should I be worried that fitting

     an Autovent will mean that I spot a leak later?

 On a pressurised system:

After the air absorbed in the water has separated (see 4 and 5, above), the best early indicator of a leak is a drop in pressure of the system, and an Autovent should, if anything, lead to a faster drop in pressure so an even earlier indication of a leak.

 On a header-tank system: