[MartinObviously]

You must bleed these engines cold with the engine off!

You need to create a header of water, I use a 2 litre bottle with the bottom cut off.

Put the bottle in the radiator cap and fill it - you can get special funnels but I can't remember what they're called. You must keep this bottle nearly full at all times.

1.) You need to bleed the radiator first, then close it when there's no bubbles.
2.) then the coolant housing (5mm hex/allen key?) then close it when it flows smoothly.
3.) then the bleed cap at the back, then close it when the coolant flows smoothly.

If you don't do it in this order, it will overheat.

Anyone who tells you another method is wrong and just got lucky that they got the air out.

Over time, the excess coolant will spill out, the "full" level is quite far down the radiator tank.

p.s having the heater on the car makes no difference, these cars don't have heater valves. the core is always open.