Error Code 3: No signal from the seal cylinder reed switch

When the heating fork moves towards the button the reed switch on the cylinder should light up 2mm before the fork touches the button shank. In order to check this though the light does need to come on therefore check the wiring at the circuit board plug. If this is correct then replace the reed switch. If the reed switch is working and in the correct position then check the free movement of the fork mechanism, the air supply and the relevant pneumatic valve.