Can anyone point me in the direction of the reason why my heater fans have stopped working?

When I left work this evening, I popped to Asda, and then to the gym...they were all working fine! When I came back out of the gym, the heater fans are now not working,...could it be a fuse?! If so does anyone know which one? If not a fuse what else could be the cause and solution?

Wrong time of year for them to stop working

Thanks