How do I remove the wax capsule from its housing?

I have a potterton puma 80 combi but the diverter valve in it has jammed causing poor CH performance but hot water is OK.

From the diverter valve I have undone the two grub screws that secures the wax assembly. Looking into the assembly there is a central pin which moves with very little force and leaks wax.

I cannot see how the wax capsule is removed from its housing. There is a large hexagonal protrusion at the end of the assembly which looks like a very thin nut but I cannot get it to turn.

How is the wax capsule removed from its housing?