bleeding

It's a plug with a hexagonal hole for an allen key - 4 or 5 mm from memory. Normal screw thread to open and close it.

edit, My memory is failing then, 6mm sounds right.
I last opened it last summer when I had to refit the heater valve. No need to take it out completely, just slacken a turn or so. Look for the coolant on the drive when it has bled.

David,

When bleeding the system I tend to have the front of the car slightly higher than the back to try and help with bleeding air out.
Make sure you have the heater valve open if you have completely emptied and refilled your coolant, otherwise you will create an air lock in that part of the system.
In fact I undo the hose from the engine block that feeds the heater circuit and fill that part up from there and reconnect when coolant is visible. Then complete filling the rest of the coolant circuit from the expansion tank.

Once there is no more air coming out of the bleed screw on the radiator, I close and run the engine for a short while until the thermostat opens.
Then re-open the bleed screw on the radiator to purge any remaining air out.

You shouldn't need to completely remove the bleed screw, however, if you do, as Rachel mentions, be careful when screwing it back in that you don't cross thread it.

Good luck.

Andy

I'm going from memory too, I *think* it's 6 mm!