I'm not sure if you solved your problem but I have a similar tap (Franke Davos in my case) and have had to replace the ceramic cartridges on two occasions over the years. On both occasions the cold tap handle slid off easily after removing the cover and the grub screw but the handle for the hot tap was stuck fast, having been 'welded' to the cartridge by the slow build up of lime scale. Eventually freed it by forcing a gap of about 1mm between handle and body with a screwdriver and then dripping descaler onto the gap. (A small piece of insulating tape wrapped around the join with a gap at the top to drip the descaler into seemed to work). This took me two days, slowing opening up a slightly bigger gap. Have now packed handle with grease and am removing it every six months to ensure no build up. Franke services were no help and a plumber suggested a new tap!
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