There is normaly a small mesh filter in the unit, that clogs up and messes around with the water flow, as doas a blocked up shower head, trouble is electric showers never get sericed, and the mesh filter is a service item
Every electric shower that I have ever used does this, it's why I hate electric heater showers. I suppose if you have one you get used to it, but we have only ever had tank fed showers.
