I have recently had my programmer replaced to a Randal 715 with
seperate controls for CH and HW.

The good news is that you appear to have a fully pumped system capable of
fully independent control. You bad news is that also appear to have selected
a complete cretin to wire up your new programmer.

Any number of wiring faults could explain the behaviour you are seeing.
Connecting one end of the thermostat to permanent live, rather than the
programmer's call for heating is one of the likely ones. Don't worry about
the lack of connection to "Htg Off". This is rarely used. The lack of
connection to one of the thermostat's terminals may be an issue, however.

Christian.