The radiator gave up on my 520i, so I fitted a new radiator, topped up the coolant and bled the system as described in the manual and a number of threads here.

No luck the engine was badly overheating and no coolant flow through the heater, classic air-lock in the heater. I tried the conventional bleeding a few more times without luck.

I then used the technique that I used to use with my previous 525i:

Allow engine to cool
Remove hose from one of the heater control valves
Using a funnel add coolant through the hose
When the funnel is full and you can't add more coolant, slowly raise the funnel until coolant pours out of heater valve
Re-connect hose
Allow the car to idle and warm up, checking heater warms up and temperature is normal
Allow engine to cool and re-check coolant level

It worked a treat - hope this helps anyone else having problems bleeding the radiator.