So the latest in a long line of faults with my car is a low coolant temp issue. I know some petrol VAG cars had issues with leaking water pumps. Is this a thing in the diesels as well?

I don't see a leaky water pump causing low coolant temps. Thermostat stuck open or faulty temp sensor is my guess.

Just now, Jorgeminator said:

I don't see a leaky water pump causing low coolant temps. Thermostat stuck open or faulty temp sensor is my guess.

Sorry I mistyped, it's a low coolant level.

13 minutes ago, Wonderloaf said:

Sorry I mistyped, it's a low coolant level.

 

Look around for dried up coolant. The residue is bright pink in color. That should point you to the source.

Head gaskets should not blow this soon, but who knows...