Here in the UK I called Franke because my mixer tap was dripping - they asked how old - if less than 5 years you get free replacements - things may be different where you live - I said 4 years and two new valve cartridges came in a few days at no cost.
There are several different models of valve cartridge - changing them is a piece of cake - you need to turn off hot and cold water first - in total a 10 minute job - Cross Point Screwdriver and an adjustable spanner.
If you go to a store to buy replacements then take one with you to ensure a match.
https://www.youtube.com/watch?v=gQHdzRnbkW4
I think Mythos is the name of a Franke Sink rather than a tap
Good luck...
March 2015