If you are in any doubt about CHANGING a Kitchen Tap Valve – do contact a professional plumber. If you have the Franke Planar Tap we have some further tips. Mixer Cartridge. the grub screw; Unscrew dome cover and locking nut; Replace cartridge; Re-assemble tap; Turn on water supply and inspect for leaks. For example, a single-handle kitchen faucet could use a ball, disc, The retaining nut must be removed to remove the faucet cartridge. © Moen.