B

External cut off switch not used in UK: Ensure nothing is plugged into red I3 connection.
▶ Connection plug for external switch contact is not plugged into control unit.
▶ There is no feedback voltage at the external safety contact of a third party condensate pump blocking the boiler.
▶ Switching point for the external temperature monitor is set too low.
▶ Connection cable to the external temperature monitor is damaged.
▶ External temperature monitor is defective.