Good idea to get the water pump and all the other gubbins in there replaced at the same time, since replacing the toothed belt means taking off the entire front bumper, which is quite an expensive job, so even if the water pump isn't about to keel over and die, replacing it at the same time is a precautionary measure.
Watch also for the water temperature gauge - if it's not reaching 90 after a few minutes' driving, the thermostat or associated parts needs to be looked at, which is also quite an expensive problem to fix, apparently.
That's new to me!
I thought the diesels took a while to warm up, mine certainly does 5-10mins in this current cold climate.
Actually my guage fluctuates between ~75-90 degrees during normal driving, never goes a smidge above 90 though, is that something to worry about?
I can't really help much more on this fault I'm afraid - forum search?
I had a 2.0 petrol until recently replacing with 2.5 tdi - the problem occurred in the last three weeks of running the petrol engine and apparently it's not uncommon. If the thermostat is not working, it will force the cooling system to work harder than it would normally, keeping the temperature low and killing your fuel economy (because it's working so hard on cooling...) My 2.0 was doing 41mpg before the fault developed and about 34 afterwards.
When I was looking for a tdi, I found at least two cars I test drove suffering the same symptoms of low temperature readings on the gauge.