Why is my Xpelair Ripple/Smooth fan turning off as soon as the switch is turned off?

There may be a couple of possible reasons

1. The switch being turned off is the electrical isolation switch, which cuts all power to the fan.
2. The timer may have reached the end of the time period. The timer on these models is a run-back timer that starts as soon as the fan is turned on via the switched live. Therefore, if the timer is set to 10 min and the fan turned on and used for 2 min, the fan will run on for 8 min, whereas if the fan is initially on for 10 min it will turn off straight away when switched off. 

Applicable models

XS100S, XS100T, XR100S, XR100T