Worcester Bosch Boiler Error Codes
If you’re experiencing an issue with your Worcester Bosch Boiler, use our Worcester Bosch Boiler Error Codes section to search by Boiler Make and Error Code to find out what the fault is.
Please enter the model name and error code:
CDI Classic Combi Boiler Error Codes
Error Code: A1
Possible Cause: Water is leaking or the pump needs replacing or freeing due to the pump running dry.
Error Code: A7
Possible Cause: The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads need checking.
Error Code: A8
Possible Cause: Break communication to FX sensor controls electrical connections need checking.
Error Code: B1
Possible Cause: Code plug not detected.
Error Code: C6
Possible Cause: Fan speed too low – the fan lead and connector need checking and may need replacing.
Error Code: E2
Possible Cause: Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.
Error Code: E9
Possible Cause: Safety temperature limiter in central heating (CH) flow has tripped the system pressure or safety temperature limiter needs checking
Error Code: EA
Possible Cause: Flame not detected due to a gas issue – the gas supply, power supply or igniter, electrode and lead need checking – contact a Gas Safe installer.
Error Code: F0
Possible Cause: Internal error – electrical connector contacts or programmer interface module – check ignition leads are not loose.
Error Code: F7
Possible Cause: Flame detected even though the appliance is switched off – check the electrode assembly is dry and the pcb and flue are clear.
Error Code: FA
Possible Cause: Flame detected after gas shut off – the gas valve needs checking – hire a Gas Safe installer.
Error Code: FD
Possible Cause: Reset button pressed by mistake – press reset button again.
CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I System Boiler Error Codes
Error Code: T1
Possible Cause: Ignition test – checking the igniter spark
Error Code: T2
Possible Cause: Fan test – checking the basic fan
Error Code: T3
Possible Cause: Pump test – checking the basic pump
Error Code: T4
Possible Cause: Three way valve test
Error Code: T6
Possible Cause: Ionisation oscillator test
Error Code: 9A 362
Possible Cause: Incorrect HCM fitted
Error Code: 9U 233
Possible Cause: Heat Control Module (HCM) error – problem with code plug
Error Code: B7 257
Possible Cause: Internal error – possible control board problem
Error Code: C6 215
Possible Cause: Fan problem – fan running too fast
Error Code: C7 214
Possible Cause: Fan problem – fan not running
Error Code: D1 240
Possible Cause: Return sensor error – sensor may be wet or damaged
Error Code: E2 222
Possible Cause: Flow sensor short circuit error
Error Code: E5 218
Possible Cause: Flow temperature too high
Error Code: E9 219
Possible Cause: Safety sensor fault – temperature too high, sensor short circuit or open circuit
Error Code: EA 227
Possible Cause: No flame detected or flame signal loss during operation
Error Code: F0 237
Possible Cause: Internal error
Error Code: F7 228
Possible Cause: Flame error – false flame or flame detected before burner started
Error Code: FA 306
Possible Cause: False flame fault – flame detected after burner stop
Error Code: FD 231
Possible Cause: Mains power fault – electrical power interruption
Error Code: FA 364
Possible Cause: Gas valve EV2 leak test failed – gas valve leak
Error Code: FB 365
Possible Cause: Gas valve EV1 leak test failed
Error Code: A1 281
Possible Cause: Pump stuck or running with air in the system
Error Code: C1 264
Possible Cause: Airflow stopped during operation
Error Code: C4 273
Possible Cause: Airflow present during last 24 hour
Error Code: D1 240
Possible Cause: Return sensor short circuit
Error Code: D4 271
Possible Cause: Temperature difference between flow and safety sensor exceeds limit
Error Code: E9 224
Possible Cause: Max thermostat activated – flue gas thermostat overheat
Error Code: EA 227
Possible Cause: No ionisation detected after ignition
Error Code: EF 349
Possible Cause: Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
Error Code: NO CODE 212
Possible Cause: Safety or flow temperature rising too fast
CDi Classic Regular Boiler Error Codes
Error Code: B1
Possible Cause: Code plug not detected
Error Code: C6
Possible Cause: Fan speed too low
Error Code: E2
Possible Cause: Central heating (CH) flow negative thermistor coefficient (NTC) sensor defective
Error Code: E9
Possible Cause: Safety temperature limiter in central heating (CH) flow has tripped
Error Code: EA
Possible Cause: Flame not detected
Error Code: F0
Possible Cause: Internal error
Error Code: F7
Possible Cause: Flame detected even though appliance switched off
Error Code: FA
Possible Cause: Flame detected after gas shut off
Error Code: FD
Possible Cause: Reset button pressed by mistake
Greenstar I System or Combi Boiler Error Codes
Error Code: 226
Possible Cause: Service tool has been connected in the blocking error history menu
Error Code: FD 231
Possible Cause: The power has been interrupted during a lockout
Error Code: C7 214
Possible Cause: Fan does not run during the start up phase – fan harness connector needs checking
Error Code: C6 215
Possible Cause: Fan speed too high – check the fan harness and connector
Error Code: C7 216
Possible Cause: Fan speed too low – check the fan harness and connector
Error Code: C7 217
Possible Cause: Fan has stopped during appliance operation
Error Code: C1 264
Possible Cause: Fan stopped during operation
Error Code: C4 273
Possible Cause: Continuous fan operation for the last 24 hours – appliance temporarily blocked
Error Code: E2 222
Possible Cause: Flow temperature sensor shorted
Error Code: E2 233
Possible Cause: Flow temperature sensor disconnected
Error Code: E9 276
Possible Cause: Primary flow temperature exceeded 95°c
Error Code: E2 350
Possible Cause: Flow temperature sensor shorted
Error Code: E2 351
Possible Cause: Flow temperature sensor disconnected
Error Code: FA 306
Possible Cause: Ionisation detected after the gas valve closed
Error Code: EA 227
Possible Cause: No ionisation detected after ignition
Error Code: F7 228
Possible Cause: Isioniation current detected before burner start
Error Code: EA 229
Possible Cause: Loss of ionisation signal during operation
Error Code: EA 261
Possible Cause: Heat control module (HCM) potentially defective – reset the appliance
Error Code: 9U 233
Possible Cause: Control box or heat control module (HCM) is defective or loose, the HCM needs to be checked
Error Code: C4 237
Possible Cause: Control box or heat control module (HCM) is defective
Error Code: F0 238
Possible Cause: Gas valve or control box error – gas valve coils need checking
Error Code: F0 239
Possible Cause: Control box or the heat control module (HCM) is defective – the control box connections need checking
Error Code: F0 242
Possible Cause: Control box or the heat control module (HCM) is defective – the HCM and control box connections need to be checked
Error Code: B7 257
Possible Cause: Control box or the heat control module HCM) is defective- the HCM and control box connections need to be checked
Error Code: F0 258
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: EH 258
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: F1 259
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: F0 262
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: F0 262
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: F1 263
Possible Cause: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
Error Code: F0 272
Possible Cause: Control box or the heat control module (HCM) is defective – control box and connections need checking or HCM might not be inserted properly and need replacing
Error Code: F0 280
Possible Cause: Control box or the heat control module (HCM) is defective – control box and connections need checking or HCM might not be inserted properly and need replacing
Error Code: F0 290
Possible Cause: Control box is defective – HCM needs checking as it might not be inserted properly or need replacing
Error Code: 328
Possible Cause: Internal error with the mains voltage – frequency may be inconsistent
Error Code: 235
Possible Cause: Incompatible heat control module (HCM) software versions – control box needs latest software
Error Code: 356
Possible Cause: Low mains voltage – the voltage may be interrupted or inconsistent and needs checking
Error Code: 360
Possible Cause: Heat control module (HCM) invalid – the inserted HCM does not correspond with the control box
Error Code: A8 362
Possible Cause: Low mains voltage – the voltage may be interrupted, inconsistent or heat control module (HCM) invalid
Error Code: CC 800
Possible Cause: Outdoor sensor defect available when accessory outdoor sensor is connected
Error Code: A1 281
Possible Cause: Pump stock or running dry
Error Code: E9 224
Possible Cause: Flue or high limit thermostat activated
Error Code: D4 341
Possible Cause: Primary flow temperature rising too fast
CDI Highflow Combi Boiler Error Codes
Error Code: A1
Possible Cause: Pump dry run detection or pump is running in air the system pressure needs checking
Error Code: A5
Possible Cause: Tank negative thermistor coefficient (NTC) defect
Error Code: A7
Possible Cause: Domestic hot water (DHW) negative thermistor coefficient (NTC) defect
Error Code: A8
Possible Cause: Energy Management System (EMS) communication error
Error Code: B1
Possible Cause: Code plug not detected
Error Code: B2, B3, B4, B5, B6
Possible Cause: Data error
Error Code: B7
Possible Cause: Burner control error
Error Code: C6
Possible Cause: Fan defect
Error Code: D3
Possible Cause: External temperature limiter
Error Code: D5
Possible Cause: Condensate pump failure
Error Code: D6
Possible Cause: Internal heat bank overflow
Error Code: EA
Possible Cause: Flame not detected
Error Code: E2
Possible Cause: Primary negative thermistor coefficient (NTC) defect
Error Code: E9
Possible Cause: Safety temperature limiter in central heating (CH) flow stat tripped
Error Code: F0
Possible Cause: Internal error
Error Code: F1
Possible Cause: ROM fault
Error Code: F7
Possible Cause: Flame detected after appliance has been shut off
Error Code: FA
Possible Cause: Flame detected after gas shut off
Error Code: FD
Possible Cause: Reset button pressed – try pressing the reset button again
Error Code: 200
Possible Cause: The boiler is in heating mode
Error Code: 201
Possible Cause: The boiler is in domestic hot water (DHW) mode
Error Code: 202
Possible Cause: The boiler is waiting – there was a heat demand from the on off or modulating control
Error Code: 203
Possible Cause: The boiler is on standby
Error Code: 204
Possible Cause: The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature
Error Code: 208
Possible Cause: The boiler is in chimney sweep mode
Error Code: 212
Possible Cause: The temperature recorded by the flow temperature sensor or the safety sensor is rising too quickly
Error Code: 226
Possible Cause: Diagnosis tool was connected and is now locked out
Error Code: 260
Possible Cause: The flow temperature sensor is not detecting a rise in temperature following a burner start
Error Code: 265
Possible Cause: The boiler is waiting in response to a heat demand – the boiler regularly switches to partial load
Error Code: 268
Possible Cause: Component test phase
Error Code: 270
Possible Cause: The boiler is modulating upwards
Error Code: 283
Possible Cause: The boiler is preparing for a burner start – the fan and pump are activated
Error Code: 284
Possible Cause: The gas valve is switched
Error Code: 305
Possible Cause: The boiler is waiting for domestic hot water (DHW) operation to end
Error Code: 235
Possible Cause: The KIM (boiler identification module) is too new for the burner control unit
Error Code: 360
Possible Cause: The KIM that has been fitted is not compatible with the burner control unit
Error Code: 9A 361
Possible Cause: The burner control unit that has been fitted is not compatible with the KIM (boiler identification module)
Error Code: 9U 233
Possible Cause: The burner control unit or KIM (boiler identification module) is faulty
Error Code: A3 317
Possible Cause: Short circuit in the flue gas temperature sensor contacts
Error Code: B7 257
Possible Cause: The burner control unit or the KIM (boiler identification module) is faulty
Error Code: C1 264
Possible Cause: No control signal or power supply to the fan during operation
Error Code: C4 273
Possible Cause: The boiler was switched off for a maximum of 2 minutes because it had been operating continuously for more than 24 hours
Error Code: C6 215
Possible Cause: The fan speed is too high
Error Code: C6 216
Possible Cause: The fan speed is too low
Error Code: C7 214
Possible Cause: The fan does not run during the start phase
Error Code: C7 217
Possible Cause: The fan speed is irregular when starting up
Error Code: CE 207
Possible Cause: Water pressure is too low
Error Code: CE 266
Possible Cause: Pump test failed
Error Code: D1 240
Possible Cause: The contacts of the boiler return temperature sensor have been short circuited
Error Code: D1 241
Possible Cause: The contacts of the boiler return temperature sensor have been interrupted
Error Code: D3 232
Possible Cause: The external switching contact has opened
Error Code: D4 213
Possible Cause: The actual temperature recorded by the flow temperature sensor or return temperature sensor is rising too quickly
Error Code: D4 271
Possible Cause: Actual temperature differential between flow and safety temperature sensor is too high
Error Code: D4 286
Possible Cause: The boiler return temperature sensor has detected a return temperature higher than 105°c
Error Code: E2 222
Possible Cause: Short circuit in the flow temperature sensor contacts
Error Code: E2 223
Possible Cause: The flow temperature sensor contacts have been interrupted
Error Code: E5 218
Possible Cause: The temperature captured by the flow temperature sensor exceeded 105°c
Error Code: E9 210
Possible Cause: The temperature measured by the flue gas sensor is too high and is open
Error Code: E9 219
Possible Cause: The safety temperature sensor has captured a temperature in excess of 105°C
Error Code: E9 220
Possible Cause: The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c
Error Code: E9 224
Possible Cause: The contacts of the safety temperature sensor have been interrupted
Error Code: E9 276
Possible Cause: The temperature flow sensor has measured a temperature in excess of 95°c
Error Code: E9 277
Possible Cause: The safety temperature sensor has measured temperature in excess of 95°c
Error Code: E9 285
Possible Cause: The boiler return temperature sensor has measured a temperature higher than 95°c
Error Code: E9 318
Possible Cause: The flue gas temperature sensor contacts have been interrupted
Error Code: EA 227
Possible Cause: An insufficient ionisation current was measured following ignition of the burner
Error Code: EA 229
Possible Cause: The ionisation current detected by the system during the burning phase was insufficient
Error Code: EA 234
Possible Cause: The contacts of the gas valve have been interrupted
Error Code: EA 261
Possible Cause: The burner control unit is faulty
Error Code: EA 269
Possible Cause: The ignition device has been activated for too long
Error Code: F0 238
Possible Cause: The burner control unit KIM (boiler identification module) is faulty
Error Code: F0 239
Possible Cause: The burner control unit KIM (boiler identification module) has an error. Cabling might have poor contact breaks and pinching or the plug and wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
Error Code: F0 242, F0 243, F0244, F0 245, F0 246, F0 247, F0 248, F0 249, F0 250, F0 251, F0 252, F0 253, F0 255, F0 259, F0 263, F0 267, F0 272
Possible Cause: The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
Error Code: F0 278
Possible Cause: The sensor test has failed – cabling and plug sensors need checking
Error Code: F0 279
Possible Cause: The burner control unit, or KIM, is faulty – control unit may need replacing
Error Code: F0 280
Possible Cause: The burner control unit is faulty
Error Code: F0 287
Possible Cause: The burner control unit, or KIM, has an error
Error Code: F0 290
Possible Cause: The burner control unit, or KIM, is faulty
Error Code: F7 228
Possible Cause: An ionisation current was measured before the burner started
Error Code: FF7 328
Possible Cause: A brief power failure has occurred
Error Code: FA 306
Possible Cause: An ionisation current was measured after the burner went out
Error Code: FD 231
Possible Cause: The mains voltage was interrupted during an interlocking fault
Error Code: EC 256
Possible Cause: The burner control unit has an error
Error Code: EH 258
Possible Cause: The burner control unit is faulty – check the plug and wiring of the burner control unit.
Error Code: H07
Possible Cause: The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode
Error Code: HrE
Possible Cause: The boiler keeps resetting
Error Code: rE
Possible Cause: The boiler resets
Greenstar Ri Boiler Error Codes
Error Code: 1 flashes 5 seconds off
Possible Cause: No boiler demand
Error Code: 2 flashes 5 seconds off
Possible Cause: Heating demand on boiler is OK
Error Code: 3 flashes, 5 seconds off
Possible Cause: No ionisation detected after ignition
Error Code: 4 flashes, 5 seconds off
Possible Cause: Loss of ionisation signal during operation
Error Code: 5 flashes, 5 seconds off
Possible Cause: Ionisation detected after burner stopped
Gas valve EV2 leak test failed
Gas valve EV1 leak test failed
Ionisation current detected before burner start
Gas valve error
Ionisation sensor shorted
Error Code: 4 flashes 5 second gap 1 long flash
Possible Cause: Sensor test failed
Error Code: 4 flashes, 5 second gap, 2 long flashes
Possible Cause: Safety temperature too high
Error Code: 4 flashes, 5 second gap, 3 long flashes
Possible Cause: Max safety thermostat activated
Error Code: 4 flashes, 5 second gap, 4 long flashes
Possible Cause: Return temperature too high
Error Code: 4 flashes, 5 second gap, 5 long flashes
Possible Cause: Flow temperature too high – supply sensor exceeded 110°c
Error Code: 1 long flash, 4 quick flashes, 5 second gap, 1 long flash, 4 quick flashes
Possible Cause: Heating control module (HCM) defective
Error Code: 2 long flashes, 4 quick flashes, 5 second gap, 2 long flashes, 4 quick flashes
Possible Cause: Fan running too fast
Fan running too slow
No airflow after defined period of time
Fan not running
Error Code: 3 long flashes, 4 quick flashes, 5 second gap, 3 long flashes, 4 quick flashes
Possible Cause: Mains voltage interrupted after locking error
Error Code: 4 long flashes, 4 quick flashes, 5 second gap, 4 long flash, 4 quick flashes
Possible Cause: Internal control board faults
Error Code: 5 long flashes, 4 quick flashes, 5 second gap, 5 long flash, 4 quick flashes
Possible Cause: All other miscellaneous faults – reset the boiler by turning the control knob anti-clockwise to the reset position
Worcester Bosch Greenstar 8000 Boiler Error Codes
Error Code: No light
Possible Cause: No power at control board
Error Code: Light on
Possible Cause: Appliance on but not operating during demand
Error Code: Slow flash ( mostly off flashes on)
Possible Cause: Ignition lockout
Error Code: Slow flash ( mostly on flashes off)
Possible Cause: Flue overheat or heat exchanger overheat
Error Code: Fast flash
Possible Cause: Volatile lockout sensor fan or code plug
Error Code: 2 pulses
Possible Cause: Check service mode switch is in minimum position
Error Code: 5 pulses
Possible Cause: Check service mode switch is in max position
Error Code: 200 O
Possible Cause: Boiler in heating mode
Error Code: 201 O
Possible Cause: Boiler in hot water mode
Error Code: 202 O
Possible Cause: Boiler in anti-cycle mode
Error Code: 203 O
Possible Cause: Boiler in standby – no heat energy demand
Error Code: 204 O
Possible Cause: Current primary water temperature higher than set value
Error Code: 208 O
Possible Cause: Chimney sweep demand
Error Code: 224 V
Possible Cause: Safety temperature limiter has tripped – top-up water until the reset pressure is reached
Error Code: 227 V
Possible Cause: No flame signal after ignition burner control unit could need replacing
Error Code: 228 V
Possible Cause: Flame signal without flame present – air/gas ratio control valve may need replacing as might the ionisation cable
Error Code: 305 0
Possible Cause: Boiler in hot water anti-cycle mode
Error Code: 306 V
Possible Cause: Flame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
Error Code: 360 V
Possible Cause: Incompatible code plug – check if a correct code plug is installed and exchange or reconnect code plug
Error Code: 815 W/B
Possible Cause: Low loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage
Error Code: 1010 O
Possible Cause: No BUS communication cable, EMS-Bus isn’t connected or damaged – connect the cable for the EMS-Bus or replace the damaged cable exchange fuse
Error Code: 1017 W
Possible Cause: Water pressure too low – the water needs topping up and the vent system or pressure sensor may need replacing
Error Code: 1021 B
Possible Cause: Hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected
Error Code: 1022 B
Possible Cause: Hot water storage temperature sensor is defective – connect the plug to the hot water temperature sensor correctly, mount the hot water temperature sensor correctly or replace the hot water temperature sensor
Error Code: 1037 W
Possible Cause: Outside temperature sensor is defective – check the connecting lead
Error Code: 1065 B
Possible Cause: Pressure sensor defective or not connected – check pressure sensor connection as it may need replacing
Error Code: 1068 W
Possible Cause: Outside temperature sensor defective – check the connecting lead
Error Code: 1073 W
Possible Cause: Short circuit of the flow temperature sensor – the temperature sensor may need replacing
Error Code: 1074 W
Possible Cause: No signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or temperature sensor could need replacing
Error Code: 1075 W
Possible Cause: Short circuit of the temperature sensor at the heating block – temperature sensor may need replacing
Error Code: 1076 W
Possible Cause: No signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead or the control unit
Error Code: 2920 V
Possible Cause: Error with the flame monitoring
Error Code: 2924 V
Possible Cause: No feedback from the modulating gas valve. The gas valve relay is defective – press the reset button and apply burner start, wait to see if fault reoccurs, if it does the gas valve needs replacing
Error Code: 2925 V
Possible Cause: Feedback from the modulating gas valve is too low
Error Code: 2927 B
Possible Cause: Flame failed during burner operation. Open the main shut off valve, shut down the appliance and check gas line, replace the ionisation electrode, set burner correctly and minimum rated load, check the integrity flue system and if the interconnected room air supply is too small, or the size of the ventilation opening is too small, clean the heating block on the flue gas side or replace the control unit/burner control unit
Error Code: 2946 V
Possible Cause: Incorrect code plug detected – the code plug needs replacing
Error Code: 2948 B
Possible Cause: No flame signal. With low output the burner starts automatically after cleaning. If the fault occurs repeatedly, the setting of the CO2 valves need checking
Error Code: 2950 B
Possible Cause: No flame signal. Following starting procedure the burner starts automatically. After cleaning set the correct gas / air ratio correctly
Error Code: 2963 B
Possible Cause: Signal from flow and heat exchanger temperature sensor outside the permissible range – the connecting lead needs connecting correctly
Error Code: 2964 B
Possible Cause: Flow rate in heat exchanger is too low
Error Code: 2965 B
Possible Cause: Flow temperature too high
Error Code: 2966 B
Possible Cause: Flow temperature rise in heat exchanger too rapid
Error Code: 2967 B
Possible Cause: Flow / heat exchanger temperature sensor differential too great
Error Code: 2970 B
Possible Cause: Pressure drop in heating system too rapid
Error Code: 2971 B
Possible Cause: System pressure too low – the heating system needs venting or water needs topping up until the preset pressure is reached. Replace the cable to the pressure sensor replace the pressure sensor