Maximum temperature of heat exchanger or circuit breaker exceeded:

No or too little flow: -- Bleed the central heating system -- Check the water pressure -- Check the heat exchanger for contamination -- Check the flow (direction, pump, valves)

Sensor not or poorly connected: -- Check the proper functioning of the sensor -- Check whether the sensor is properly mounted

Bad connection: -- check the wiring

Defective sensor: -- replace sensor if necessary

No or too little air supply:-- check the air supply

No or too little flue gas discharge: check the flue gas discharge. Recirculation: -- replace the gaskets