Coolant leak?

[fishphone]

Definite slow coolant loss 2019 40TDI 48k miles (1/3 litre over 250 miles). No visible signs of an actual leak. Checked oil filler cap, normal. Is this a common issue? Been advised not to put any of the propietory radiator sealant liquids in. Car still under extended warranty, would this be covered please. Any help appreciated

[Magnet]

Hello Steve,

Common issue? - I would be sure not. Abnormal? -yes. This car should not use anything like that amount of coolant in a year, let alone 250 miles. 
Simply get this investigated under your extended warranty, without any DIY investigation or fiddling. Warranty company? 
Could be as simple as a faulty reservoir cap, or anything more serious from there. 
Perhaps you could let us know how you get on. 
Kind regards,

Gareth.

[Steve Q]

I agree with Gareth, you need to be speaking to the warranty company asap. As Gareth has suggested it could be something as simple as the expansion tank cap not sealing properly. 

[fishphone]

Confirmed water pump, being replaced under warranty