Engine light on

Hi, I have a 2018  octadia 2.0 TDI,I currently have the engine management light displayed and have a code P26F800 coolant pump c stuck but no overheating issue.From cold temp gauge rises to 3 bars, drops to zero then climbs steady to 90 degrees where it then stays.When codes are cleared light does not come back on from cold but if I do a short run , stop for around an hour and restart light comes back on.I have checked temp with diag tool and found gauge starts to rise at 60 degrees and drops to 48 degrees when needle drops to 0.I have taken it to a VW specialist who after having it for a day said water pump needs changing as it is leaking but there is no leak whatsoever.Any help will be greatly appreciated.