Compatible Dyson DC24 washable HEPA post filter

When would this part need replacing?
After the motor has failed
When the pre filter has not been washed often enough causing this filter to block too.
When the filter cover pops out from the ball
When the machine makes a noise like a balloon going down when you switch it off (air leak).

Fits The following DC24 models:
DC24, DC24i, DC24 Multi floor, DC24 Multi floor Complete, DC24 Multi Floor exclusive, DC24 Animal, DC24 Blitz it, DC24 DRAWING Limited edition

Compatible Dyson DC24 HEPA post filter FIL311