posted this 02 January 2018
Is the pump a Standard or Universal?
If it is a Universal pump it should be starting instantly so it sounds faulty.
If the pump is a Standard pump, it sounds like you are struggling to get enough flow through to activate the pump. Certainly if you turn the shower on and the water dribbles, or there is no water, you need a Universal pump. If the pump starts when you place
a magnet next to the arrow on one of the flow switches of the pump then the pump is ok and something is restricting the flow under gravity and creating a megative head.