Should I blame my shower, or should I blame hard water?

Hi I live in London SE1, a hard water area. I am on my second electric shower (the same model) in the space of about 10 years. The water got so hot coming out of the shower head that it was impossible to have a cool to warm shower in the hot summer months with the first one that I changed. The same is happening with this one after 3 years. My question is, Would a water conditioner fitted between the shower and the shower feed solve the problem or would it be something to do with cleaning something inside the shower box, like perhaps the solenoid? Thanks