won't be nothing to do with pressure if your loosing power aswell.
its an electrical issue.
what model shower is it ?
does it have a power on light on the front case ?
just cause the pull cord light stays on don't mean the wire from the pullcord to the shower isn't faulty or loose.
its a common problem with electric showers as they draw som much power any loose connections may be blackened where they are arcing.
hi-spec plumbing & heating (essex)
July 2009