low water out put from the shower head?

I have a aqualisa quartz a2 (ipx4). the pump has been over time getting noisier with out any obvious problems but now the water pressure from the shower head seams to have dropped. normal setting would appear to be gravity type pressure and when you select boost on the remote, it boost`s a little but not like it used to. are there any filters that might need cleaning or descaling? or would it be more intensive ? cheers paul