No heating and the engine overheating?

It sounds like you have an air pocket in the cooling system, after the completed the work did you allow the engine to warm up fully heat up before installing the radiator cap? I have seen people jack the front of the car up to help remove the air bubbles. Also, I have seen a water pump impeller fall of the water pump on less expensive replacements. If you had a stuck thermostat the heater should still work most of the time. I would remove the upper radiator hose and start the engine, (coolant still in system) to see if coolant is forced out of the hose. Also, you can remove the thermostat and put it in boiling water to see if it opens.

Hi and thanks for the reply.

I did let the engine warm up at idle to operating temperature, and even after pumping the big hose I could reach without burning myself, the radiator hoses were cold, but there was minor circulation between the inlet and return of the coolant tank, just none to the matrix or radiator.

It did this when the leak from the pump bearing went and was leaking badly, but the coolant tank stayed at max the whole time and had circulation.

I'm taking the double thermostat off to have a look for anything obvious, and to check as best as possible, the hoses as well, but I've ordered one anyway if it looks like I can't fix it.

Update, please see video.

The weirdest thing about this, is when I squeeze the top radiator hose, the coolant tank surges accordingly...ish,

It looks like a previous owner has added radweld at some point, I've only had the car 18months, and have only added coolant, but did notice the slightly brownish tint to the coolant in the tank and confirmed by horrid white gravel/gel stuff when taken the pump and thermostat off.

Though strangely, not much on the pump side, but loads on the thermostat side?

Yep, you are onto something with the thermostat, I would replace it and the problem should go away. Thanks for the video it helps. Have a good weekend and let me know what happens.

In the video, the dual thermostat is off the engine and all coolant pipes that could be accessed were flushed with hosepipe until completely clear, then move on to next pipe until all run clear in all directions.

I even started the engine with the thermostat off, and coolant tank stayed full, no drain down at all.

Aaahh well, the car is booked in to a garage from tomorrow, we know them well, and it should be done by next weekend.

Thank you to all who replied, I will update with news of anything found or end result.

Sounds good, please let us know, have a good weekend.