I've just taken it apart. The valve arm seems quite smooth in motion. The reason why it was going nuts and not switching off the motor is because the switch has been crushed in!
You can just about see the circled switch is pushed all the way in.
Know a trick trick to fix it or a where to find a new switch to solder in?
Do you know what the part number is? (It's the one on the top I need not the one on the side)
And if I put it back but make sure valves are open will this cause any problems if I continue to drive it?