Horstmann Centaur C21 To British Gas Hive

[Jonnylogan85]

Hi!

Trying to replace Horstmann Centaur C21 to British Gas Hive. The wiring is confusing me a little... The existing wiring as attached picture. The control unit is connected to a Horstmann HRT3 thermostat.

Any suggestions as to how to wire up, greatly appreciated....