We regularly get called out to look at showers which are not functioning satisfactorily. Often the complaint is the temperature cannot be regulated or it is stuck on warm etc. Quite often this is a simple job of replacing the thermostatic cartridge. The difficult part is identifying the make and model of the shower. Occasionally we have to dismantle the shower and take a photo of the cartridge and then go online and see if when can identify the correct cartridge from a supplier.
sometimes we are unable to identify the cartridge at all.
Also, its not always obvious how the shower dismantles so keeping any instructions supplied with the shower is a must.
If you are having a new shower installed (or taps) please, please, please keep a note of the manufacturers name and the model of the shower and a date of when it was installed. It will make all our lives a lot easier.
A note to manufacturers too, could you please put some form of identification on your brass-ware, it would help tremendously and boost your spares sales.