it has 3.5 bar RWC written on the front of the black cartridge
The valve is leaking from the front end of the black cartridge (not the thread which connects to the brass metal body of the valve). The way I see it I just need to find a new cartridge. I can shut off the water unscrew the cartridge and screw on a new one.
Does anyone have any thoughts on this please, are they any considerations that I should be taking into account?
I'm not sure of the mains feed arrangement with the Ariston cylinder but you may have to drain it to remove the pressure reducer. You will certainly have to release the internal pressure after you have turned off the mains.
Get hold of a replacement pressure regulator preferably one fitted with a pressure gauge - you can then check and adjust if required.
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