HSI drifting

[Stacker]

Hi,

 

This may be a bug or I've not configured things correctly - after about 10 minutes of flying I notice that my HSI is completely off when compared to my wet compass. It also starts to rotate very slowly so it becomes impossible to use. The course deviation is still accurate (when I'm flying an ILS for example), it's just the heading that's wrong.

 

Is there a way of resetting the HSI heading to align it back to the wet compass/mag north?