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Code | Description | Possible Cause |
F1 | Ignition fault (lockout) Boiler failed to light |
No gas Insufficient gas Incorrect gas valve adjustment Electrode ignition lead defect Electronic igniter defective Check air inlet duct Check connections to igniter unit |
F4 | Ignition fault (lockout) went out when lit | As F1 possible cause |
F5 | Overheat fault |
Overheat stat operated Maximum temperature exceeded Check thermistor connections Air in system with thermistor at maximum setting Faulty overheat stat connection Check that pump is wired into appliance and not programmer. This would cause no pump overrun |
F6 | Central heating flow thermistor fault |
Thermistor cable defective/broken, thermistor faulty. Check that thermistor attached correctly to pipe |
F7 | Domestic hot water thermistor fault |
Thermistor cable defective/broken, thermistor faulty. Check that thermistor attached correctly to pipe |
F9 | Water pressure sensor fault |
Faulty sensor connection Check wiring |
F10 | Central heating return thermistor fault |
Thermistor cable defective/broken, thermistor faulty. Check that thermistor attached correctly to pipe |
F11 | Main board connection fault | Check wiring between mainboard and user interface |
F12 | User interface connection fault | Check wiring between mainboard and user interface |
F13 | Main PCB connection fault | Check connections and wires |
F14 | Central heating flow temperature is greater than 95 degrees |
System fault Possible pump failure Check thermistor on flow |
F16 | Flame detection fault (flame presence for more than 5 seconds after burner stop) | Gas valve defective |
F17 | Power supply is less than 170V | Check electrical supply/polarity |
F18 | User interface fault | Faulty user interface |
F19 | Central heating thermistor unplugged | Check thermistor connection |
F20 | Software incompatibility | Incorrect user interface or main PCB |
F24 | Central heating return temperature is greater than 90 degrees |
System fault Possible pump failure Check thermistor on return |
F25 | Maximum temperature rise slope |
Possible pump failure Air in system |
F26 | Maximum delta temperature |
Check thermistor on return System - too restrictive |