Hi,

On CH2 the pipe going upwards from the bend on the right goes upwards
and is then capped with an air vent as you say. I think its a good idea
to go into the loft and see whats happening. Ive got a mate coming
around on Saturday who knows a little and I'll put your comments into
the mix and try and work it out. I'll also test the air coming out for
hydrogen.

On CH2, the pipe from the left of the motorised pump must feed the
radiators. However, where is the return to the boiler if this valve if
only the hot water is switched on?

Also, why is the pipe from the left of the valve connected to the pipe
going upwards from the pump?

I wonder why air gets trapped in this one radiator however? This is the
last radiator on the circuit.

Also, consider this. If the air is moving around the system (you can
hear it bubble through the boiler and a few seconds after that the pump
starts cavitating - so it is moving around) then it must at some point
go through the coil in the DHW tank. I appreciate this doesnt solve the
cause of the problem but is it possible to fit some sort of bleed
filter to the bleed valve at the 15mm pipe coming off the 22mm where it
enters the cylinder?

In addition, if air is getting in then this must be pushing water out.
I presume back into the expansion tank in the loft.

The only other thing I have noticed is that my towel radiator has a
slight leek. A couple of little drips that does build up to around 2
table spoons fulls of sugar over the course of the weekend. Could this
be the route of the problem?

One more question: which way would the water flow through the pump?
From top to bottom or pumped upwards from bottom to top.

Unfortunately I work away all week so I am limited to looking at the
thing in the limited time I get at home at weekends

CM.