Bleeding airlock problem

[Steth]

I have an airlock in the CH feed to the conservatory (wasn't a problem when we filled it for the first time, but is now after draining the system.) The pipes run at loft floor level (above the kitchen ceiling ) in copper and then change to plastic and loop up and over to run down inside the cavity wall to emerge at floor level in the conservatory. The airlock is plainly at the top of the plastic loop(s).
1. Do I have to fit a bleed valve at the top of the plastic loop (more difficult) or can I get away with teeing in a vertical length of copper from the horizontal run of copper as long as it rises higher than the plastic loop (much easier)?

2. Either way, will I have to do the flow, return or both?

Thanks in anticipation.

 

[chrishutt]

The pipes run ...down inside the cavity wall

Definitely not a good idea to run pipes in the cavity wall. What if the pipes freeze, leak or burst? I suggest you have a rethink of the run.

 

[Steth]

Sorry, I should have been clearer - the cavity is no longer an external wall. It was, but is now the wall between the kitchen and conservatory. It just seemed neater than having the pipes running down the wall visible. Any ideas on the airlock problem?