How do I replace a refillable CO2 cartridge of a tap water cooler?

Is there little fizz on the water (sparkling water not good)? Is the pressure gauge lower than 3.5 bar? Time to replace the CO2 cartridge.

1. Unscrew the pressure gauge from the empty bottle (this may release some gas).
2. Keep the bottle separate and hand it over during the next maintenance
3. Remove the seal of the new CO2 cartridge
4. Screw the pressure gauge on the new cartridge
5. Open the bottle and the pressure gauge is automatically back at 4 bar.