The comms between the OTB and the CTL over radio consists of 5 messages.

1. Every 30 seconds increment counter.
2. Every 60 seconds Boiler Relative Modulation and Flame Status.
3. Every 5 minutes Control Set Point.
4. Every 5 minutes several OT information exchanged.
5. Every 20 minutes some like of Heat Demand.

It is that 2nd message that stops being requested by the CTL from the OTB, if there is an OTB on the OT Bus. The comms between the OTB and the Boiler appear to be unchanged.