Thanks for all your help so far.

I'll check the heater matrix tomorrow and see how that goes.
Also now, I let the engine rest for a few mins, the coolant in the expansion tank dropped so I topped it back up and let it run again.
The engine heats up still, not as quickly as it did, but still heats up then the fan kicks in and cools it back down again. There is pressure building in the system still and stays there when its hot.

And also, now all the pipes to the heater control valve are hot.

So, after emptying the system.
I slowly filled it back up with the coolant, upto the max line and when it stayed there, I started the engine and let it run for a bit, keeping it topped up. Thats pretty much it.

I replaced the lid and left the engine running, the coolant level dropped so I slowly undone the lid and topped up some more.

I also held onto the accelerator cable a bit to increase the revs a bit, and that also helped bleed the system, I saw some air coming up through the system, so topped up again.

Thats pretty much it.
I left it to idle for 10 mins, the fan kicked in once or twice, and then i switched off the engine. The coolant level in the expansion tank I noticed was rising up a bit, maybe 10mm then falling again, continuously.

Thats all I did apart from drive it round the block.

I bet this is all wrong, it would be my luck

Cheers