Identify your appliance
Models and ranges Bulex Selected references from manufacturer documentation, including older generations. Check the full name and suffix on the rating plate: manuals and error codes can differ by version and country.
Boiler display
Bulex error codes Check the model, note the full code and learn the useful precautions before the diagnosis.
Before reading the list S displays are often operating states. This general list does not cover every generation: on older ThermoMaster F24E, FAS28E and F28E, F22 means excessive pressure and F21 insufficient pressure. Check the exact manual before topping up; see our F22/F28 article linked on the brand page.
28 error codes found
S.00 Heating: no heat demand This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.02 Heating pump pre-run This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.03 Burner ignition in progress This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.04 Burner running This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.07 Pump overrun This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.08 Burner anti-cycling time This display describes the appliance’s normal operating state (standby, pump pre-run, ignition, burner running…). It is not a fault. View details S.37 Fan malfunction The fan is not running at the expected speed or does not stop: a dirty or worn fan, wiring or the electronic control. View details S.41 Water pressure too high The circuit pressure is too high: overfilling, a worn expansion vessel or strong heating of the circuit. View details S.42 Heat demand blocked by an internal malfunction A control, communication or electronic memory fault has been detected: circuit board, controller, wiring or power supply. View details S.53 Safety function triggered by lack of water The water pressure in the heating circuit is too low, often because of a small leak, recent radiator bleeding or a slow loss over the months. View details S.54 Appliance on standby due to lack of water The water pressure in the heating circuit is too low, often because of a small leak, recent radiator bleeding or a slow loss over the months. View details F.00 Flow temperature sensor faulty or badly connected A temperature sensor is sending an impossible value: a faulty sensor, or a loose or short-circuited cable or connector. View details F.01 Return temperature sensor faulty A temperature sensor is sending an impossible value: a faulty sensor, or a loose or short-circuited cable or connector. View details F.10 Flow temperature sensor short circuit A temperature sensor is sending an impossible value: a faulty sensor, or a loose or short-circuited cable or connector. View details F.11 Return temperature sensor short circuit A temperature sensor is sending an impossible value: a faulty sensor, or a loose or short-circuited cable or connector. View details F.20 Safety temperature limiter tripped A temperature safety has tripped: the water is not circulating enough (air, pump, closed valves, dirty filter or heat exchanger) or the circuit is short of water. View details F.22 Low-water protection The water pressure in the heating circuit is too low, often because of a small leak, recent radiator bleeding or a slow loss over the months. View details F.23 Flow/return temperature difference too large Water circulation is insufficient or detected as abnormal: air in the circuit, a blocked or weak pump, closed valves or a dirty circuit. View details F.24 Abnormally fast temperature rise Water circulation is insufficient or detected as abnormal: air in the circuit, a blocked or weak pump, closed valves or a dirty circuit. View details F.25 Flue gas temperature too high A temperature safety has tripped: the water is not circulating enough (air, pump, closed valves, dirty filter or heat exchanger) or the circuit is short of water. View details F.27 False flame signal The appliance detects a flame when the burner should be off, or after the gas has closed. The gas valve or the sensing circuit may be faulty. View details F.28 Burner fails to start The burner failed to light or the flame was not detected: interrupted gas supply, worn ignition or sensing electrode, gas valve or condensate drain. View details F.29 Re-ignition impossible after flame loss The flame went out during operation: disturbed air supply or flue, unstable gas pressure or a dirty sensing electrode. View details F.32 Fan fault The fan is not running at the expected speed or does not stop: a dirty or worn fan, wiring or the electronic control. View details F.49 Undervoltage on the eBUS link A control, communication or electronic memory fault has been detected: circuit board, controller, wiring or power supply. View details F.61 Gas valve control fault A control, communication or electronic memory fault has been detected: circuit board, controller, wiring or power supply. View details F.63 Electronic memory (EEPROM) fault A control, communication or electronic memory fault has been detected: circuit board, controller, wiring or power supply. View details F.75 No pressure change detected when the pump starts Water circulation is insufficient or detected as abnormal: air in the circuit, a blocked or weak pump, closed valves or a dirty circuit. View details See the Bulex codes
