How can I fix my creda shower unit?

My Creda shower unit is displaying the following problems:
Red light does not illuminate immediately when hot selected.
Low pressure when turned to hot setting.
Red light switches off when running and water turns cold. (this occurs constantly).
Sorry but i do not know the model no, but i would imagine it is the previous model to the 550c as it looks similar in design. Any feedback would be appreciated as replacing for a new unit is not an option.