Any experts on the Honeywell CM Zone heating control system?

I can't get my HR80 radiator controller modules to communicate with an
existing HC60NG relay module. The CM67z room unit and three HR80's were
bought as a pack in Germany recently. The HC60NG boiler control unit
came with a CM67NG RF room controller (model reference T6667D1081),
bought about four years ago in the UK.

The CM67z will correctly set the HR80 programmable temperatures and the
CM67z can communicate with the HC60NG, at least if I set parameter
17:SU to 1 or 2 (which automatically sets 7:tS to 2) before doing the
binding. However the CM67z with the factory default settings won't bind
to the HC60NG. The HR80's won't switch the HC60NG output ON whatever
temperature I set manually. I've tried clearing all the bindings and
running through all the teach-ins from zero but I am still stuck.

Any ideas? I wonder if the HC60NG is too old to receive data from the
HR80's but I don't want to go and invest £60 in a new HC60NG if it is
not the problem.