excessive bubbling noises in pipes

[mondial]

I live in a two storey flat with a 16 year old central heating system. which is incredibly noisy when turned on. There is the noise of air bubbling up the pipes, prticularly loud upstirs.
I have a potterton ideal neterheat, 8 radiators (four up and four down), a hot water tank in the airing cupboard with a grundfos pump, running at full speed. In the loft is a header(?) tank.
The ball valve appears to work perfectly with 4 inches of water in the tank. The 4 upstairs radiators heat up along with two of the downstairs ones. Two downstairs furthest from the boiler and pump do not work unless we close off two upstairs ones, when they heat up. There is no air in the radiators, just clean water. Any ideas?

However, the major problem is the noise of air in the pipes which is very loud and happens when the system is turned on by the timer, twice a day. This noise is almost continuous for 3the first 0 minutes or so.
I have bled the pump with the big central screw. In the airing cupboard, between the hot water tank and the three way valve is a bleed screw, which lets out a little air when undone.
The advent of the noise coiincides with the fitting of a three way valve last year.
Any help would be appreciated.

 

[Paul Barker]

Well posted, very descriptive.

The problem is that the air can't get out while the pump is on. Usual arrangement is the flow from the boiler has a T with open vent off it, then a cold feed then a pump. The area between the boiler and the pump, where we expect air to be released by the system, is a low pressure zone, which has the effect of trapping the air in. The simple fix is to replace the 22mm T with a 28mm T, the expansion at this point allows the air to release. A better solution is an air seperator.

If you have some other arrangement change it to this arrangement.

 

[madm]

Where can I get an 'air separator'? It sounds as if it might be the solution to my problem, or at least a help...

 

[Paul Barker]

about 12 quid at plumber merchants. They aren't the solution to all vagueries of open vent heating systems but they are a help. You have to be able to solder as they all take solder connections, available in 28mm or 22mm. Diagram on the box explains it all.

BnQ probably has them. Also try Screwfix they may do them.

 

[kevplumb]

11 squid

 

[madm]

Thank you for the gen on air separators...

I've got one that looks like a tuba...

... the air separator.