Worcester Bosch (Greenstar range)
EA 227: Ignition failure. The boiler has tried to light and failed. Can be caused by a faulty gas valve, blocked burner, or electrode issue. Try resetting once. If it returns, book a repair.
EA 229: Flame lost during operation. The boiler lit but the flame went out. Often a gas supply issue or faulty flame sensor. Do not keep resetting repeatedly.
D5: Low water pressure detected. Check your pressure gauge. If it's below 1 bar, repressure using the filling loop. If it keeps dropping, there's likely a leak.
E9: Safety temperature limit reached. The boiler has overheated. Can be caused by a pump failure, sludge buildup, or blocked heat exchanger. Needs professional diagnosis.
A1: No hot water from a combi boiler. Usually a diverter valve issue. Needs an engineer.
Vaillant (ecoTEC range)
F28: Ignition failure. The most common Vaillant fault. Can be gas supply, ignition lead, electrode, or gas valve. Reset once. If it persists, do not keep trying.
F75: Pressure sensor fault. The boiler cannot detect a pressure change when the pump starts. Often caused by a faulty pump or pressure sensor. Common on older ecoTEC models.
F22: Low water pressure. The boiler has detected pressure below the minimum. Repressure using the filling loop. If it drops again within a few days, there's a leak somewhere.
F27: False flame detection. The boiler thinks it can see a flame when there isn't one. Usually a faulty flame sensor or PCB issue. Needs an engineer.
F29: Flame extinguished during operation. Similar to F28 but happens mid-cycle. Often a flue or gas supply issue.
Ideal (Logic, Vogue, Esprit range)
L2 (or F2): Ignition lockout. The boiler failed to ignite after multiple attempts. Gas valve, electrode, or burner issue. Reset once and monitor.
L1 (or F1): Low water pressure. Pressure has dropped below 0.5 bar. Repressure via the filling loop to between 1 and 1.5 bar.
L5: False flame. The PCB is detecting a flame signal when the boiler should be off. Usually a PCB fault. Needs professional diagnosis.
L8: Return thermistor fault. The sensor reading the return water temperature has failed. Needs replacement.
LC: Pump fault or no circulation. The boiler is firing but water isn't moving through the system. Could be a seized pump, airlocked system, or blockage.
Baxi / Main
E133: Ignition fault. Gas supply issue, faulty electrode, or gas valve problem. The most common Baxi error code. Reset once.
E119: Low water pressure. Repressure the system. If it keeps dropping, check for leaks at radiator valves, connections, and under the boiler.
E125: Circulation fault. No flow detected. Could be a pump failure, airlock, or system blockage. Often accompanied by banging or gurgling noises.
E110: Overheating. The boiler has hit its safety temperature limit. Can be sludge in the heat exchanger, pump issues, or a blocked system. Do not reset repeatedly.
E160: Fan fault. The fan isn't running at the correct speed. Needs professional diagnosis, usually a fan or PCB replacement.
Viessmann (Vitodens range)
F4: Ignition failure. Similar causes to other brands, gas supply, electrode, or valve. Reset once via the OK button.
F5: Flame lost during operation. Flue issue, gas pressure drop, or faulty flame detector.
F2: Burner lockout. The boiler has locked out for safety. Needs a reset and investigation if recurring.
B1 or 0C: Low pressure warning. Repressure the system. Viessmann boilers often show a bar graph rather than a numeric code for pressure issues.
Glow-worm (Energy, Easicom range)
F1: Low pressure. Repressure to 1-1.5 bar.
F4: Ignition failure. Gas supply, electrode, or valve issue.
F9: Fan speed fault. The fan isn't reaching the required RPM. Needs professional diagnosis.
F22: Dry fire. The boiler has fired without sufficient water flow. Potentially dangerous. Do not reset. Call an engineer.
Alpha (E-Tec, InTec range)
E10: Low pressure. Repressure the system.
E20 or E28: Ignition failure. Reset once. Persistent faults usually mean a gas valve or electrode issue.
E40 or E41: Flue blockage or fan fault. The boiler cannot verify safe flue gas discharge. Do not attempt to fix yourself.
If your error code isn't listed here, check your boiler manual or search online for your specific model and code. If the error keeps returning after a reset, don't keep trying.