Siamp Concealed Systern slow filling problem

[Army of Daves]

Hi
My Siamp Intra 50/99B concealed cistern has started filling extremely slowly. I read on this forum that some cisterns fill slowly because of debris, which should be an easy fix, except mine is concealed making it impossible to see into. See images. As a total novice I don't want to go poking about too much and breaking it completely by accident.
Any ideas how to solve this issue?
Dave

 

[CBW]

Likely the inlet washer has failed (usually a split/hole), try replacing it 1st, should be easy enough

 

[Rodders53]

No slow filling is typically the result of a split in the diaphragm of the fill valve. Easy to replace (isolate the cold water feed in first).

https://shop.siamp.co.uk/diaphragm-washer-5 and how to videos https://www.youtube.com/user/siampshop