Water filter problem

Afternoon Everyone.
We have a water filter fitted as per the photo attached and have changed the three filters in the lower sections. The water now flows normally for only a few seconds before it reduces to a mere trickle. Should I change anything on the top two sections? The kits you can buy from Leroy Merlin only have the three filters. I’ve never seen replacements for the upper sections for sale anywhere.
Does anyone have any ideas as to why my flow is reduced? ( No jokes about it being due to my age please!)

We had a similar filter and a similar problem. Peter came and fitted a new system which now works well. His contact number is 00 34 694 49 96 30

I have a system the same as yours. The filters you buy are in packs of 4, 3 for the canisters and one for across the top. There is one other, I can’t recall the type but it is in a blue box and is the most expensive. Recommend you change all five filters.
Without seeing the tap, two possible causes, one might be the diaphragm ruptured in the large white water holder under the sink. Or the other is, I can only guess that the pipe to the tap is clogged up with something.
While the system is disconnected from the mains water, open the tap and try blowing down the tap, to see if anything comes out the pipe. Maybe if you have a spare piece of pipe, that you can attach to the mains water tap and flushing down the chrome end of the tap. with tap pipe in a bucket.
Maybe ive made it sound like hard work but what I’m suggesting is very simple, and would only take a few minutes. All being well that will be all that’s needed. Good luck

Thanks both of you for your help.

Leroy Merlin and Brico Depot both sell the Post Filter and Membrane separately to the Filters. Should you need a Tank, hopefully not, Leroy certainly used to stock them too. For future reference it's cheaper to buy Pack of 4 filters.

Thanks VMW