I expect that this system is open vented and the pipe above the boiler is
the over flow for the little (10 litre) F&E cistern.

A few photos of the pump / boiler area would help a lot.

I'll snap a dig photo later and post it. Need to move out a lot of junk from
the cupboard :-)

The pipework need fixing to stop the air entering and before other
problems get too serious.

Suspected that - will order and replace the two faulty radiators. I was
putting it off as the weeping on is a large one in the lounge, biggest in
the house :-(

The valve in the cellar is a drain point - the washers often weld
themselves in place and opening the valve only allows water out from the
middle of the washer.

Okay, won't worry about that too much then.

Cheers, Rob.