To be fair, as dan correctly points out, mine has additional coolant pipes, and had its own challenges
but the same routine should be followed.
Drain.
Refill slowly (The manual quotes a Litre per minute rate).
DO at least 3 cycles of
-allowing the engine to warm,
- several cycles of 10 second 3000 rpm bursts
- allow to cool to 50c
whilst heater is at different settings.