I'm not at home right now so I don't have access to MES but I did manage a few checks... The tank was pressurized when I opened it, the fan does come on (didn't have time to warm the car up, but I triggered it with air con) and the hoses are warm (even from the drive here).

Also my heater works always, even when the temperature spiked... I guess I'll have to book a mechanic

I have been to the mechanic and he'll take a look when he gets the chance.

I'm slightly less worried now because he said if the water pump was on its way out, the heating wouldn't work.

It was the water pump after all... It's now swapped, along with the timing belt, ribbed belt and other bits and pieces that go along with it.

Since he was doing the timing belt, he also removed the intake manifold and took out the swirl flaps. The car is much more responsive now, because the boost leak is eradicated. It's a very fun engine again to drive.