can anyone tell me how to remove the cover from the rear heater in my 1.6td Multivan!

As far as I can see, I have removed all the screw's & the seat base!
I thought that all I would have to do then was pull it forward & off!
But it wont come off & I cant see what is stopping it! (it does move a little bit but seem to be catching on something!)
After the 'V' belt breaking & the engine overheating I have replced the melted coolant flanges on the Head & refilled the coolant/bled the rad!
but there still seems to be some air in the system!

(I have driven it for a couple of miles & it drives lovely with the temp guage going upto & staying just below halfway! but when I got back & checked everything It sounded like a load of air bubbles moving around in the coolant pipes!!)
So I am presuming that I have to bleed the rear heater under the rear seat!
Is this correct or do I need to do something else aswell?