| F.00 | Fault with flow temperature sensor. NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness or NTC sensor defective. |
| F.01 | Fault with return temperature sensor. NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness or NTC sensor defective. |
| F.10 | Short circuit flow temperature sensor. NTC defective, short circuit in the cable harness, cable or casing. |
| F.11 | Short circuit return temperature sensor. NTC defective, short circuit in the cable harness, cable or casing. |
| F.12 or F.91 | Short circuit cylinder temperature sensor. NTC defective, short circuit in the cable harness, cable or casing. |
| F.13 | Short circuit domestic hot water cylinder temperature sensor. NTC defective, short circuit in the cable harness, cable or casing. |
| F.20 | Safety switch off. Overheating temperature reached. Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge via ignition cable, ignition plug or ignition electrode. |
| F.22 | Safety switch off. Low water pressure in the boiler. Insufficient or no water in the boiler, water pressure sensor defective or cable to the pump or to the water pressure sensor is loose, not connected or defective. |
| F.23 | Safety switch off. Temperature difference too great NTC1/NTC2. Pump blocked, insufficient pump output, air in boiler or flow and return NTC sensor connected the wrong way round. |
| F.24 | Safety switch off. Temperature rise too fast. Pump blocked, insufficient pump output, air in boiler, system pressure too low or non-return valve blocked or incorrectly installed. |
| F.25 | Safety switch off. Flue gas temperature too high. Break in plug connection for optional flue gas safety temperature limiter (STB) or break in cable harness. |
| F.27 | Safety switch off. Fault in flame detection. Moisture in the electronics, electronics flame monitor defective or gas solenoid valve is leaking. |
| F.28 | Ignition unsuccessful when starting up. Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, incorrect gas restrictor, incorrect spare gas valve, fault on gas valve, multiple plug on PCB incorrectly plugged in, break in cable harness, ignition system defective, isolation current interrupted, incorrect earthing or electronics defective. |
| F.29 | Flame loss. Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product or ignition transformer has spark failure. |
| F.32 | Fan frost protection function active. Fan speed outside tolerance values. Plug or fan not plugged in correctly, multiple plug on PCB not plugged in correctly, break in cable harness, fan blocked, hall sensor defective or electronics defective. |
| F.33 | Fan frost protection function active. Air pressure switch fault. Pressure monitor has not switched or has switched at fan speed value that’s too high (insufficient air supply). Pressure monitor not plugged in correctly, pressure monitor defective, hose removed from between the pressure monitor and silencer or air/flue pipe blocked. |
| FA9 | eBUS fault. Voltage too low. Short circuit on eBUS, eBUS overload or two power supplies with different polarities on the eBUS. |
| F.61 | Gas valve control system fault. Short circuit to earth in cable harness for the gas valve, gas valve defective (colls shorted to earth) or electronics defective. |
| F.82 | Gas valve switch-off control fault. Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas valve leaking or electronics defective. |
| F.83 | EEPROM fault. Electronics defective. |
| F.64 | Fault with electronics, sensor or analogue to digital convertor. Flow or return NTC short circuited or electronics defective. |
| F.85 | Electronics temperature too high. Electronics overheating due to external influences or electronics defective. |
| F.67 | Valve sent back by ASIC is incorrect. Implausible flame signal or electronics defective. |
| F.88 | Unstable flame (analogue input). Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restrictor or ionisation flow interruption. |
| F.70 | Invalid product code (DSN). Display and PCB replaced at same time and Device Specific Number not reset or wrong or missing output range coding resistance. |
| F.71 | Fault with flow/return temperature sensor. Flow temperature sensor signalling constant value, flow temperature sensor incorrectly positioned on supply pip or flow temperature sensor defective. |
| F.72 | Deviation in the water pressure sensor/return temperature sensor. Flow/return temperature difference too great. Flow and/or return temperature sensor defective. |
| F.73 | Water pressure sensor not connected or has short circuited. Interruption or short circuit of water pressure sensor or interruption or short circuit to GND in supply line to water pressure sensor or water pressure sensor defective. |
| F.74 | Electrical problem in the water pressure sensor. Line to water pressure sensor has a short circuit to 5V/24V or internal fault in the water pressure sensor. |
| F.75 | Pressure sensor fault. Pressure switch defective. |
| F.78 | Safety cut-out in primary heat exchanger is defective. Safety cut-out feedback does not match the gas valve feedback. |
| F.77 | Condensate or smoke. No response, flue non-return flap defective. |
| F.78 | Interruption to DHW outlet sensor at external controller. UK ink box is connected but hot water NTC not bridged. |
| F.83 | Fault with burner temperature sensor. When burner starts, the temperature change registered at the flow or return temperature sensor is non-existent or too small. Insufficient water in product or the flow or return temperature is in the wrong position on the pipe. |
| F.84 | Fault with flow/return temperature sensor. Valves not consistent. Flow and return temperature sensors signalling implausible values. Flow and return temperature sensors have been inverted or have not been correctly installed. |
| F.85 | Fault with temperature sensor. The flow and/or return temperature sensors have been installed on the same pipe – temperature sensor not connected or is connected incorrectly. |
| F.86 | Underfloor heating contact is open or sensor is defective or disconnected. |
| F.87 | Electrodes not connected or are connected incorrectly or short circuit in the cable harness. |
| F.88 | Gas valve fault. Gas valve not connected or is connected incorrectly or short circuit in the cable harness. |
| F.89 | Pump fault. Pump not connected or is connected incorrectly, incorrect pump connected or short circuit in the cable harness. |
