Code	Meaning	Cause
F.49	eBUS fault	Short circuit on the eBUS, eBUS overload or two power supplies with different polarities on the eBUS
F.52	Mass flow sensor connection fault	Mass flow sensor not connected/disconnected, plug not connected or incorrectly connected
F.53	Mass flow sensor fault	Mass flow sensor faulty, filter below venturi filter cap wet or blocked, gas flow pressure too low
F.54	Gas pressure fault (in combination with F.28/F.29)	No or too little gas supply pressure, gas valve closed
F.56	Fault: Mass flow sensor regulation	Gas valve defective, cable harness to gas valve defective
F.57	Fault during comfort safety mode	Ignition electrode highly corroded
F.61	Fault: Gas valve regulation	Short circuit/short to earth in cable harness for the gas valve Gas valve defective (coils shorted to earth) Electronic defective
F.62	Fault: Gas valve switch-off delay	Delayed shutdown of gas valve Delayed extinguishing of flame signal Gas valve leaking Electronics defective
F.63	EEPROM error	Electronics defective
F.64	Electronics/NTC fault	Supply or return NTC short circuited, electronics defective
F.65	Electronic temperature fault	Electronics overheating due to external influences, electronics defective
F.67	Electronics/flame fault	Implausible flame signal, electronics defective
F.68	Unstable flame signal fault	Air in gas, gas flow pressure too low, wrong air ratio, condensate route blocked, wrong gas restrictor, ionisation flow interruption (cables, electrodes), flue gas recirculation, condensate route
F.70	Invalid device specific number (DSN)	Spare part case: Display and PCB replaced at same time and DSN not set, wrong or missing output range coding resistor
F.71	Flow NTC fault	Flow temperature sensor signalling constant value: Flow temperature sensor incorrectly positioned at supply pipe Flow temperature sensor defective
F.72	Flow/return NTC fault	Flow/return NTC temperature difference too great → flow and/or return temperature sensor defective
F.73	Water pressure sensor signal in the wrong range (too low)	Interruption/short circuit of water pressure sensor, interruption/short circuit to GND in supply line to water pressure sensor or water pressure sensor defective
F.74	Water pressure sensor signal outside correct range (too low)	Cable to water pressure sensor has short-circuitedd at 5V/24 V or internal fault in water pressure sensor
F.75	Fault, no pressure change detection when starting pump	Water pressure sensor and/or pump defective, air in heating installation, too low water pressure in boiler; check adjustable bypass, connect external expansion vessel to return
F.76	Overheating protection on primary heat exchanger has responded	Cable or cable connections for safety fuse in primary heat exchanger or primary heat exchanger defective
F.77	Flue non-return flap/condensate pump fault	No response from flue non-return flap or condensate pump defective
F.78	Interruption to DHW outlet sensor at external controller	UK link box is connected, but hot water NTC not bridged
F.83	Flow and/or return temperature sesnsor temperature change fault	When the burner starts, the temperature change registered at flow and/or return temperature sensor is non-existant or too small. Not enough water in the boiler Flow and/or return temperature sensor not in correct position at pipe
F.84	Fault: Flow/return temperature sensor difference implausible	Flow and return temperature sensors return implausible values Flow and return temperature sensors have been inverted Flow and return temperature sensors have not been correctly fitted
F.85	Fault: Flow and return temperature sensors incorrectly fitted	Flow and/or return temperature sensors have been fitted to the same pipe/wrong pipe
F.92	Coding resistor fault	The coding resistor on the PCB does not match the entered gas family. Check the resistor, repeat the gas family check and enter the correct gas family.
F.93	Gas group fault	Combustion quality outside the permitted range: Wrong gas restrictor, recirculation, wrong gas family, internal pressure measuring point in venturi blocked (do not use lubricant on O-ring in venturi.). Gas family check prematurely terminated.
Communication fault	No communication with PCB

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