A: I am not exactly sure which Axis you have, if it is the thermo then yes you will need a cartridge (see below) if it is the digital version then you are probably going to need a new processing unit.
You will have to find out which cartridge you have.
Pink for a combi or multipoint and grey any system with balanced (equal) pressures.
Remove the on/off knob should just pull forward however it can be a bit of a bu**er then remove the 4 screws that hold the temperature knob in place, remove the temperature knob and then you will see the colour of your cartridge.
If you already have the cartridge and want to carry on and replace it you will have to turn the water off to the shower.
Then remove the cartridge you will need to remove the 4 large screws at the side of the cartridge these have posidrive or ‘Torx’ T25 heads depending on there age.
Pull the cartridge forward to remove.
Before fitting the new cartridge you should replace the small ‘O’ ring at the rear of the body this is another bu**er to change……(something like a crochet hook or the sort of thing that dentists use will help)
It is not always necessary to replace this ring however if there any problems with the cartridge, the first question you will be asked is did you replace the ‘O’ ring? if the answer is no! then you will be told to phone back once it has been replaced.
When you refit the cartridge make sure that the slot, (usually on the right of the body ) the gasket and the body all line up properly then retighten the screws.
On the older versions you have to reuse the original brass screws if you have this type be careful not to over tighten the screws because the brass inserts in the body may split, on a few occasions you may find they have split when you remove the old cartridge if this happens then you will probably have to replace the body.
Refit the temperature control knob (new screws supplied) the fit the on / off knob, turn the water back on and check for leaks, if everything is OK remove clothes and have a shower!!!