Stiff Self closing mixer taps?

[Illuminate]

I tried to fix stiff self closing taps but could not work it out. I do not have the brand of taps. The very top came off like a lid but the actual head did not seem to come off inside the lid It appeared as like a bleed point like on a radiator. I could also access the cartridge further down and cleaned it up as well as releasing pressure from the part that appeared like a bleed point but no luck. Please can someone help?

 

[Illuminate]

The taps appeared like this one

 

[ShaunCorbs]

Swap them for new as they get scaled up internally

 

[JoshThanks]

Swap them for new as they get scaled up internally

Thanks for your response, That's what I thought. If they get replacements then I guess I can advise them on getting a electrolytic limescale inhibitor but would this just need to be installed onto the hot feed?

 

[Illuminate]

On a row of these taps on the hot side water was barely coming out but I fixed the issue for all but am not 100% sure what fixed it.
I thought it could be a blockage but first dismantled the tap, then I started on the first tap and tested the pressure when disconneting part the isolation valve before the flexi and non return valve. When I turned the isolation on while it was disconnecting, water burst out, then slowed and then made a slight gurgling sound and was powerful again. I did not notice anything other than water come out. Could this of been a airlock and I thought this way would not clear an airlock. The system is run of a fortic cylinder? Any knowledge would be great to help me understand better.

Thanks