Baxi DUO TEC Boilers
55 fault codes documented
E09 — Gas valve connection fault
The boiler has detected a problem with the electrical connection to the gas valve, which controls gas flow to the burner.
E10 — External probe fault
The boiler's external temperature probe is reporting an issue. This probe helps the boiler regulate heating based on outside conditions.
E11 — External RF probe fault
The boiler's wireless (RF) external temperature probe is reporting a fault. This probe helps the boiler regulate heating based on outside conditions.
E12 — Water flow switch fault (still open)
The boiler's differential water flow switch indicates that there is no water flow when there should be, or it's stuck in an open position.
E13 — Water flow switch fault (still closed)
The boiler's differential water flow switch indicates that water is flowing when it shouldn't be, or it's stuck in a closed position.
E15 — Gas valve command fault
The boiler's main control board (PCB) is unable to correctly command or communicate with the gas valve.
E18 — Water refill active
This message indicates that the automatic water refill function is currently active. This is a status message, not a fault, and means the boiler is topping up its water levels.
E19 — Maximum water refill time exceeded
The boiler's automatic water refill function has exceeded the maximum allowed time, suggesting a problem with filling the system.
E20 — Central heating NTC sensor fault
The boiler's sensor for the central heating flow temperature is faulty, either short-circuited or open-circuited.
E28 — Flue NTC sensor fault
The boiler's flue gas temperature sensor is faulty, either short-circuited or open-circuited.
E40 — Return central heating NTC sensor fault
The boiler's sensor for the central heating return temperature is faulty, either short-circuited or open-circuited.
E50 — DHW NTC sensor fault (tank boiler)
The boiler's sensor for the Domestic Hot Water (DHW) temperature, specifically for tank versions, is faulty.
E53 — Obstruction in the flue pipe
The boiler has detected a blockage or obstruction in the flue pipe, which is critical for safe exhaust gas venting. This fault can lead to a lockout if not resolved promptly.
E55 — Main control board (PCB) requires calibration
The boiler's main control board (PCB) has not been set or calibrated, which is necessary after replacement or certain system changes.
E62 — Antiwind activation, increased fan speed
The boiler has detected wind conditions affecting the flue and has increased the minimum fan speed to compensate. This is usually a normal operational message, not a fault.
E63, E65, E69 — Combustion level out of range
The boiler's combustion levels are outside the acceptable range, which can affect efficiency and safety. This might be related to fan speed or flame signal correction.
E66 — Flue duct obstruction at minimum power
The boiler has detected an obstruction in the flue duct when operating at its minimum power setting.
E67 — Antiwind activation at maximum power
The boiler has detected wind conditions affecting the flue while operating at maximum power.
E68 — Gas pressure instability
The boiler has detected an unstable gas supply pressure, which can lead to inefficient operation or ignition problems.
E70 — Flame signal problem or micro interruption
The boiler is experiencing issues with its flame detection system, including possible brief interruptions of the flame signal.
E71 — Fan parameter out of range in autocalibration
During the automatic calibration process, the fan speed parameter was detected to be outside the acceptable operating range.
E72 — Combustion test out of range in autocalibration
During the automatic calibration process, the combustion test results were found to be outside the acceptable range.
E73 — Modified Flame signal
The boiler has detected a modified flame signal. This is a diagnostic message and typically does not require user action.
E77 — Current out of range
The boiler's internal current measurements, often related to flame detection, are outside the expected range.
E78 — Minimum gas valve current out of range
The boiler has detected that the minimum current supplied to the gas valve is outside its normal operating limits.
E79 — Maximum gas valve current out of range
The boiler has detected that the maximum current supplied to the gas valve is outside its normal operating limits.
E83-87 — Communication error with room unit
The boiler is unable to communicate correctly with the room thermostat or other room control units.
E92 — Combustion test alarm during auto-setting
The boiler's self-calibration process has triggered an alarm during the combustion test, indicating a problem with combustion.
E109 — Pre-circulation alarm
The boiler has detected an issue during the pre-circulation phase, which is when the pump runs before ignition to prepare the system.
E110 — Boiler max temperature exceeded (overheat)
The boiler has detected that its internal temperature has exceeded a safe maximum limit, either rapidly (gradient) or due to general overheating. This often triggers a safety thermostat.
E110 flashing - Overheat or faulty thermostat
The boiler's safety thermostat has activated, indicating an overheat condition or a fault with the thermostat itself. This can prevent the boiler from operating safely.
E117 — Water pressure too high
The boiler has detected that the primary heating circuit water pressure is too high, exceeding 2.7 or 2.9 bar.
E118 — Water pressure too low
The boiler has detected that the primary heating circuit water pressure is too low, less than 0.5 bar.
E125 — Water circulation fault
The boiler has detected an issue with water circulation in the primary heating circuit, often indicated by a lack of temperature change after ignition or rapid temperature changes.
E127 — Antilegionella temperature not reached
The boiler has failed to reach the required temperature for the Antilegionella function, which purifies the domestic hot water tank.
E128 — Flame failure during operation
The boiler has experienced a flame failure during normal burner operation, meaning the flame extinguished unexpectedly.
E129 — Frequent loss of flame during ignition
The boiler has repeatedly lost its flame during the ignition sequence, even with maximum correction attempts.
E130 — Flue thermostat sensor tripped (lockout)
The flue thermostat sensor has tripped, indicating excessively high temperatures in the flue, leading to a boiler lockout.
E133 — Gas supply fault or ignition failure
The boiler has failed to ignite, indicating a problem with the gas supply or the ignition system. This includes cases where the condensate trap is frozen or blocked.
E134 — Gas valve open, no gas detected
The boiler's gas valve opened, but no flame was detected within the allowed time, indicating a lack of gas or an ignition issue.
E135 — Gas valve connection fault or internal error
The boiler has detected an issue with the gas valve connection or an internal fault on the main control board (PCB).
E154 — Plausibility test (flow/return) failure
The boiler's system has failed a plausibility test between the flow and return temperatures, suggesting an issue with water circulation or sensor readings.
E160 — Fan fault
The boiler has detected a problem with the fan, which is essential for proper combustion and flue gas extraction.
E178 — Low temperature safety thermostat tripped
The low temperature safety thermostat has tripped, indicating that the boiler or system water temperature is too low for safe operation or has dropped unexpectedly.
E270/161 — Dry fire or overheat prevention activated
The boiler has activated its dry fire or overheat prevention system, indicating a risk of damage due to lack of water or excessive temperature.
E317/162 — Wrong power supply electrical frequency
The boiler has detected an incorrect electrical frequency (Hz) from the main power supply.
E321/163 — Domestic Hot Water NTC sensor fault
The boiler's sensor for the Domestic Hot Water (DHW) temperature is faulty, either short-circuited or open-circuited.
E384/164 — Fault flame (parasitic flame)
The boiler has detected a 'parasitic flame,' meaning it senses a flame when there shouldn't be one, or detects a flame signal incorrectly.
E385/165 — Under voltage
The boiler has detected that the incoming electrical power supply voltage is too low.
E430/166 — Water pressure test failed
The boiler's water pressure test (either temporary or final) has failed, indicating a problem with the system's water circulation or pressure.
E431/167 — Aluminium sensor fault
The boiler's aluminium sensor (likely a temperature sensor) is faulty, either short-circuited or open-circuited.
Boiler not firing - Fan jammed or faulty
The boiler is attempting to ignite but fails, or makes unusual noises. This suggests a problem with the internal fan, which is essential for proper air-fuel mixture and exhaust.
Display not illuminated - Boiler has no power or a circuit fault
The boiler's control panel display is completely dark and unresponsive. This indicates a loss of electrical power to the boiler or a critical internal electrical fault.
No hot water or heating - Boiler pump not circulating water
The boiler is not providing heating or hot water, and the circulation pump may not be operating. This prevents hot water from reaching radiators or taps.
CH system pressure less than 0.5 bar or more than 2.7 bar - Incorrect heating system pressure
The central heating system pressure is outside the normal operating range, either too low or too high. This condition can prevent the boiler from functioning correctly and may lead to system shutdown.