Glow worm ultimate won't fire?

Just lately, my GW ultimate will not fire up (every time) after being off during normal use. Off for thermostat - no relight , off for timer - no relight.

BUT... if I tap the little silver switch housing very gently, it fires. I really do mean gentle btw hardly any force. In fact, one time it switched on when I just touched the box.

Any guesses what the problem might be? DIY job? r is the gas supply involved?