Thanks Dumbrill, I'd rather take out the existing clock.
Presumably you still have the blanking plate to go back in the hole left by the clock?
Wiring in the CM927 Relay box
Disconnect the clock from Terminal Block X2
Insert a link between X2/1 and X2/4 (L)
Connect relay box L to X2/4 (L)
Connect Relay box N to X2/5 (N)
Remove link between X9/7 and X9/8
Connect Relay box A to X9/7
Connect Relay box B to X9/8
Do
NOT insert a link between L and A in the relay box.
You must use 0.5mm or 0.75mm heat resistant 4-core plus earth cable, e.g Tower Brand from B&Q/Electrical wholesaler/Plumbers' merchant.
The earth wire is not used and should be cut back to the outer sleeve at both ends.
Mounting Relay box
As well as following the instructions about location, you need to check that there is reliable communication between controller and relay box. The easiest way to do this is to connect a lead to the L and N terminals of the relay with a 3-pin plug on the other end and plug in. Hold relay and controller in proposed positions and follow instructions in the installation manual for RF communication check.