It sounds like the pump isn't working full power or not at all and what's coming out is only gravity pressure. I cannot give any solutions but you can check the mira website
www.mirashowers.com and click on Contact Mira
then take it from there enter your details and what the problem is.
If the answer is a new shower then unfortunately the new government regulations on electrical installations, that came in to force last week, means you will have to get an electrician who is conversant with installing electric showers.
Don't mess with water and electrics unless you know exactly what you are doing. You only live once.
Sorry can't be anymore useful.
Bob
BOB
January 2005