The water doesn't flow (decalcified already)

Hello!

I have this (sorry, couldn't find on international/USA version) coffee maker, and recently it completely stopped making espresso. It started with normal "scale" sympthoms (slower preparation), I tried to run twice the citric acid descaler, but now, if I switch the trigger to flow, the machine just makes intense sound of working boiler, but only a few drips soak the coffee in the holder. Interestingly, when I try to do that with citric acid, it manages to flow.

What I tried:

- cleaned 2 or 3 times with citric acid (30-40 g of dry concentrate / liter)

- disassembled the (not sure if correct word) piston where the water comes out, took the screw and spring, cleaned them, reinstalled.

- cleaned both metal filters

From what I learned reading this forum, possibly I would want to make much more concentrated acid and try it. Or try a commercial descaler. But is the trouble really here? I can see plenty of different spare parts in local e-shops for this model, but what could be the problem...

P.S. The machine is abt. 10 years old, descaled about yearly, and what specifically surprises me - I only used bottled water for last 2-3 years preparing coffee in it.