Timing belt replacement for 1.4TDI engine.

Next Monday, the time has finally come: due to 'rattling noises' from the timing belt/tensioner/water pump, and this has been the case since day one, my Polo will finally receive a new timing belt for the camshaft and a new water pump.
After a colleague of mine had the same thing replaced on his Léon last week, and then the car broke down, I wanted to ask you what they might have 'broken' in the workshop, or what I should check after the replacement!

Hello Joohn,

If you want to control everything perfectly, you can almost do the change yourself...
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Unfortunately, you didn't mention how many kilometers your engine has. However, if you hear noises coming from the belt drive, I would recommend replacing all (!) of the tension/idler pulleys and the water pump (if it is driven by the timing belt).
Please do not use cheap replacement parts from the cheap repair chain with the 3 letters. What they were planning to give me as "spare parts" would immediately end up in the trash for me.

Hello, Rainer

Thank you for your response!

While I may claim to 'understand' diesel engines, I am not actually skilled enough to handle the repair myself.
I am satisfied with the performance of my engine, although it tends to lose some power above 3500 RPM. Whether this has something to do with a late factory setting, I can't say for sure right now, but I'll check it out later, assuming they know what they're doing!
By the way, my car has 66,000 km on it, and all the belts and pulleys, as well as the water pump, will also be replaced. This also means that it is still under warranty!