HOW CAN I FIX MY MASTER SWITCH?

My Worcester Bosch greenstar 24i/28i junior boiler is not working - the green pilot light went out so I turned off the boiler so I could turn it back on. The switch doesn't work - if I hold the switch in it works fine (I get hot water, heating works, etc) and there are no flashing lights saying I have a fault - but the switch won't stay on. Is this mendable?