shower pump runs on

We recently had a Monsoon twin positive head pump .... first of all - it's great (almost)!

However, we have a problem that when we turn off the shower the pump runs on for anything up to 10 seconds. With the shower turned off, if I wiggle the shower thermostat, then it will stop the pump running.

I first thought it might be a faulty flow sensor on the pump, but this doesn't appear to be the case. Whilst the pump is running on (after the shower is turned off), if I close the valves installed close to the pump then the pump will instantly stop.

Any ideas what's going on and how to fix it?

thanks

monsoon what one ?

standard 3.5 bar twin

Could be air, run the shower with the pump switched off for a couple of minutes or so, using full hot then full cold, then turn the pump back on again and see if it's cured.

or check.
Reed clamp out of position.
Jammed flow switch.
Faulty reed switch or P.C.B.