Worcester Bosch Boilers
60 fault codes documented
A1 — Water leak or pump dry run
The boiler has detected a water leak, or the pump is running dry or with air in the system. This can lead to pump damage if not addressed.
A1 281 — Pump stuck or running dry
The boiler's pump is either stuck or running dry, possibly with air in the system. This can lead to inefficient heating or pump damage.
A3 317 — Flue gas temperature sensor short circuit
There is a short circuit in the contacts of the flue gas temperature sensor. This indicates a fault with the sensor responsible for monitoring flue gas temperatures.
A5 — Tank NTC sensor defective
The negative thermistor coefficient (NTC) sensor for the hot water tank is faulty. This sensor measures temperature and affects hot water operation.
A7 — Hot water sensor defective
The domestic hot water (DHW) negative thermistor coefficient (NTC) sensor or its connecting leads are defective. This will affect the boiler's ability to provide hot water.
A8 — sensor communication error
There is a break in communication to the FX sensor controls. This indicates an electrical connection issue preventing proper sensor operation.
A8 362 — Low mains voltage or invalid HCM
This code indicates either low or inconsistent mains voltage, or an invalid Heat Control Module (HCM). The boiler's electrical supply or its internal control unit may have a problem.
B1 — Code plug not detected
The boiler's code plug has not been detected. The code plug is essential for the boiler's correct operation as it identifies the boiler type and settings.
B2-B6 — Data error
The boiler has encountered a data error, indicating a problem with internal data processing or storage. This can prevent the boiler from functioning correctly.
B7 — Burner control error
The boiler's burner control unit has detected an error. This unit is responsible for managing the ignition and operation of the burner.
B7 257 — Internal error or control module problem
This code indicates an internal error, possibly related to the boiler's control board or the Heat Control Module (HCM). The HCM or its connections may be defective.
C1 264 — Fan stopped or no control signal
The boiler's fan has stopped operating or is not receiving a control signal or power supply. Proper fan function is crucial for safe combustion.
C4 237 — Control box or HCM defective
The control box or Heat Control Module (HCM) is defective. These components manage the boiler's overall operation.
C4 273 — Airflow present / continuous fan operation
This indicates that airflow was present continuously for the last 24 hours, or the boiler was switched off for a short period due to continuous operation. The appliance may be temporarily blocked.
C6 — Fan speed too low or fan defect
The boiler's fan speed is too low, or there is a general fan defect. This can hinder proper combustion and flue gas exhaust.
C6 215 — Fan running too fast
The boiler's fan is operating at an excessively high speed. This indicates a problem with the fan or its control system.
C6 216 — Fan speed too low
The boiler's fan speed is too low. This can prevent proper combustion and flue gas expulsion.
C7 214 — Fan not running during start phase
The boiler's fan is not running, particularly during the start-up phase, or at all. This prevents the boiler from igniting safely.
C7 216 — Fan speed too low
The boiler's fan speed is too low. This issue can prevent proper air supply for combustion and safe exhaust of flue gases.
C7 217 — Fan stopped or irregular speed
The boiler's fan has stopped during appliance operation or its speed is irregular during startup. This indicates a critical fault with the fan system.
CC 800 — Outdoor sensor defect
The outdoor temperature sensor, if connected, is defective. This sensor helps the boiler adjust its output based on external temperatures.
CE 207 — Water pressure too low
The boiler's water pressure is too low. This is a common issue that prevents the boiler from operating safely and efficiently.
CE 266 — Pump test failed
The boiler's internal pump test has failed. This indicates a problem with the pump itself, which circulates water through the heating system.
D1 240 — Return sensor error or short circuit
The boiler's return temperature sensor has an error, or its contacts are short-circuited. The sensor might also be wet or damaged, affecting accurate temperature readings.
D1 241 — Boiler return temperature sensor contacts interrupted
The contacts of the boiler return temperature sensor have been interrupted. This means the boiler is not receiving proper temperature feedback from the return line.
D3 — External temperature limiter activated
The external temperature limiter has been activated, preventing the boiler from operating. This is a safety feature to prevent overheating.
D3 232 — External switching contact opened
An external switching contact has opened. This contact could be part of an external control device connected to the boiler, causing it to stop operating.
D4 213 — Flow/return temperature sensor rising too quickly
The actual temperature recorded by the flow or return temperature sensor is rising too quickly. This indicates a potential overheating issue or sensor malfunction.
D4 271 — Flow/safety sensor temperature difference exceeds limit
The temperature difference between the flow and safety sensors has exceeded the permissible limit, or is too high. This is a safety measure to prevent overheating.
D4 286 — Boiler return temperature sensor detected temp higher than 105°c
The boiler return temperature sensor has detected a temperature exceeding 105°C. This is a critical safety warning indicating potential overheating in the return circuit.
D5 — Condensate pump failure
The condensate pump has failed. This pump is essential for removing acidic waste water from high-efficiency boilers.
D6 — Internal heat bank overflow
The boiler has detected an internal heat bank overflow. This indicates a problem with the internal hot water storage or expansion system.
E2 — CH water flow NTC sensor defective
The central heating (CH) water flow negative thermistor coefficient (NTC) sensor or its connection leads are defective. This sensor monitors the temperature of water flowing out for heating.
E2 222 — Flow sensor short circuit
The flow temperature sensor contacts are short-circuited. This means the sensor is sending an incorrect or constant signal, which affects the boiler's ability to regulate temperature.
E2 223 — Flow temperature sensor contacts interrupted
The flow temperature sensor contacts have been interrupted. This means the boiler is not receiving any temperature feedback from the flow line.
E2 233 — Flow temperature sensor disconnected
The flow temperature sensor is disconnected. This prevents the boiler from accurately measuring the water temperature leaving the boiler.
E2 350 — Flow temperature sensor shorted
The flow temperature sensor has shorted. This indicates a fault in the sensor or its wiring, leading to incorrect temperature readings.
E2 351 — Flow temperature sensor disconnected
The flow temperature sensor is disconnected. This prevents the boiler from accurately measuring the water temperature leaving the boiler.
E5 218 — Flow temperature too high
The boiler's flow temperature is too high, or the temperature captured by the flow temperature sensor has exceeded 105°C. This is a critical safety fault.
E9 — Safety temperature limiter tripped
The safety temperature limiter in the central heating (CH) flow has tripped. This is a critical safety measure, often due to high system pressure or an overheating issue.
E9 210 — Flue gas sensor temperature too high and open
The temperature measured by the flue gas sensor is too high, and the sensor circuit is open. This is a critical safety fault indicating excessive flue gas temperatures.
E9 219 — Safety sensor fault or temperature too high
A safety sensor fault has occurred, indicating that the temperature is too high or the sensor has a short circuit or open circuit. This is a safety mechanism to prevent damage.
E9 220 — Safety temperature sensor shorted or too high (>130°c)
The safety temperature sensor contacts have shorted, or the sensor has detected a temperature exceeding 130°C. This is a critical safety lockout.
E9 224 — Max thermostat activated or flue/high limit thermostat activated
The maximum thermostat has been activated, often due to a flue gas thermostat overheat or activation of the high limit thermostat. This is a safety shutdown.
E9 276 — Primary flow temperature exceeded 95°c
The primary flow temperature has exceeded 95°C. This indicates a potential overheating issue in the boiler's main heating circuit.
E9 277 — Safety temperature sensor measured temperature in excess of 95°c
The safety temperature sensor has detected a temperature above 95°C. This is a critical safety measure to protect the boiler from overheating.
E9 285 — Boiler return temperature sensor measured temperature higher than 95°c
The boiler return temperature sensor has measured a temperature above 95°C. This indicates potential issues with heat dissipation or sensor accuracy.
E9 318 — Flue gas temperature sensor contacts interrupted
The contacts of the flue gas temperature sensor have been interrupted. This means the boiler cannot accurately monitor flue gas temperatures for safe operation.
EA — Flame not detected or lost
The boiler's flame was not detected or the flame signal was lost during operation. This often points to an issue with the gas supply or ignition system.
EA 227 — No ionisation detected after ignition
No ionisation current was detected following the ignition of the burner. This means the boiler failed to confirm the presence of a flame after attempting to light.
EA 229 — Loss of ionisation signal during operation
There was insufficient ionisation current detected by the system during the burning phase, or a general loss of ionisation signal. This indicates the flame is not consistently detected.
EA 234 — Gas valve contacts interrupted
The contacts of the gas valve have been interrupted. This means the gas valve is not able to open or close correctly, preventing gas flow to the burner.
EA 261 — Heat control module (HCM) or burner control unit faulty
The Heat Control Module (HCM) is potentially defective or the burner control unit is faulty. This module is vital for managing the boiler's operation.
EA 269 — Ignition device activated for too long
The ignition device has been activated for an excessive duration. This indicates that the boiler is attempting to ignite the flame but is unsuccessful.
EC 256 — Burner control unit has an error
The burner control unit has detected an error. This unit is critical for safe ignition and supervision of the boiler's flame.
EF 349 — Central heating boil detected
A central heating boil has been detected. The boiler is operating at minimum burner load with a temperature difference greater than 18°C between flow and return.
EH 258 — Burner control unit or HCM faulty
The burner control unit or the Heat Control Module (HCM) is faulty. This indicates a problem with the core electronic components managing the boiler.
F0 — Internal error (electrical/programmer/ignition)
An internal error has occurred, potentially related to electrical connector contacts, the programmer interface module, or loose ignition leads. This indicates a general malfunction within the boiler's electronics.
F0 237 — Internal error
An unspecified internal error has occurred within the boiler's system. This suggests a general malfunction of the control electronics.
F0 238 — Gas valve or control box error
The boiler has detected an error with the gas valve or the control box. This could mean the gas valve coils need checking or there's a problem with the burner control unit (KIM).