Worcester Bosch Combi Boiler Error Codes

Worcester Bosch CDI Classic Combi Boiler Error Codes Is your Worcester Bosch boiler displaying an error code? Find out what it means in our complete error code list.

Worcester Bosch Combi Boiler Error Code Solutions

Fault Description System Behaviour
A1Water is leaking or the pump needs replacing or freeing due to the pump running dry.
A7The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads need checking.
A8Break communication to FX sensor controls electrical connections need checking.
B1Code plug not detected .
C6Fan speed too low – the fan lead and connector need checking and may need replacing.
E2Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.
E9Safety temperature limiter in central heating (CH) flow has tripped the system pressure or safety temperature limiter needs checking
EAFlame not detected due to a gas issue – the gas supply, power supply or igniter, electrode and lead need checking – contact a Gas Safe installer.
F0Internal error – electrical connector contacts or programmer interface module – check ignition leads are not loose.
F7Flame detected even though the appliance is switched off – check the electrode assembly is dry and the pcb and flue are clear.
FAFlame detected after gas shut off – the gas valve needs checking – hire a Gas Safe installer.
FDReset button pressed by mistake – press reset button again.

Worcester Bosch CDI Highflow Combi Boiler Error Codes

Fault DescriptionSystem Behaviour
A1Pump dry run detection or pump is running in air the system pressure needs checking
A5Tank negative thermistor coefficient (NTC) defect
A7Domestic hot water (DHW) negative thermistor coefficient (NTC) defect
A8Energy Management System (EMS) communication error
B1Code plug not detected
B2, B3, B4, B5, B6Data error
B7Burner control error
C6Fan defect
D3External temperature limiter
D5Condensate pump failure
D6Internal heat bank overflow
EAFlame not detected
E2Primary negative thermistor coefficient (NTC) defect
E9Safety temperature limiter in central heating (CH) flow stat tripped
F0Internal error
F1ROM fault
F7Flame detected after appliance has been shut off
FAFlame detected after gas shut off
FDReset button pressed – try pressing the reset button again

Worcester Bosch CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system Boiler Error Codes

Fault DescriptionSystem Behaviour
T1Ignition test – checking the igniter spark
T2Fan test – checking the basic fan
T3Pump test – checking the basic pump
T4Three way valve test
T6Ionisation oscillator test
9A 362error – incorrect HCM fitted
9U 233Heat Control Module (HCM) error – problem with code plug
B7 257Internal error – possible control board problem
C6 215Fan problem – fan running too fast
C7 214Fan problem – fan not running
D1 240Return sensor error – sensor may be wet or damaged
E2 222Flow sensor short circuit error
E5 218Flow temperature too high
E9 219Safety sensor fault – temperature too high, sensor short circuit or open circuit
EA 227No flame detected or flame signal loss during operation
F0 237Internal error
F7 228Flame error – false flame or flame detected before burner started
FA 306False flame fault – flame detected after burner stop
FD 231Mains power fault – electrical power interruption
FA 364Gas valve EV2 leak test failed – gas valve leak
FB 365Gas valve EV1 leak test failed
A1 281Pump stuck or running with air in the system
C1 264Airflow stopped during operation
C4 273Airflow present during last 24 hour
D1 240Return sensor short circuit
D4 271Temperature difference between flow and safety sensor exceeds limit
E9 224Max thermostat activated – flue gas thermostat overheat
EA 227No ionisation detected after ignition
EF 349Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212Safety or flow temperature rising too fast

Worcester Bosch CDi Classic Regular Boiler Error Codes

Fault DescriptionSystem Behaviour
B1Code plug not detected
C6Fan speed too low
E2Central heating (CH) flow negative thermistor coefficient (NTC) sensor defective
E9Safety temperature limiter in central heating (CH) flow has tripped
EAFlame not detected
F0Internal error
F7Flame detected even though appliance switched off
FAFlame detected after gas shut off
FDReset button pressed by mistake

Worcester Bosch Greenstar I System / Combi Boiler Error Codes

Fault DescriptionSystem Behaviour
226Service tool has been connected in the blocking error history menu
FD 231The power has been interrupted during a lockout
C7 214Fan does not run during the start up phase – fan harness connector needs checking
C6 215Fan speed too high – check the fan harness and connector
C7 216Fan speed too low – check the fan harness and connector
C7 217Fan has stopped during appliance operation
C1 264Fan stopped during operation
C4 273Continuous fan operation for the last 24 hours – appliance temporarily blocked
E2 222Flow temperature sensor shorted
E2 233Flow temperature sensor disconnected
E9 276Primary flow temperature exceeded 95°c
E2 350Flow temperature sensor shorted
E2 351Flow temperature sensor disconnected
FA 306Ionisation detected after the gas valve closed
EA 227No ionisation detected after ignition
F7 228Isioniation current detected before burner start
EA 229Loss of ionisation signal during operation
EA 261Heat control module (HCM) potentially defective – reset the appliance
9U 233Control box or heat control module (HCM) is defective or loose, the HCM needs to be checked
C4 237Control box or heat control module (HCM) is defective
F0 238Gas valve or control box error – gas valve coils need checking
F0 239Control box or the heat control module (HCM) is defective – the control box connections need checking
F0 242Control box or the heat control module (HCM) is defective – the HCM and control box connections need to be checked
B7 257Control box or the heat control module HCM) is defective- the HCM and control box connections need to be checked
F0 258Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
EH 258Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F1 259Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F0 262Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F1 263Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F0 272Control 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
F0 280Control 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
F0 290Control box is defective – HCM needs checking as it might not be inserted properly or need replacing
328Internal error with the mains voltage – frequency may be inconsistent
235Incompatible heat control module (HCM) software versions – control box needs latest software
356Low mains voltage – the voltage may be interrupted or inconsistent and needs checking
360Heat control module (HCM) invalid – the inserted HCM does not correspond with the control box
A8 362Low mains voltage – the voltage may be interrupted, inconsistent or heat control module (HCM) invalid
CC 800Outdoor sensor defect available when accessory outdoor sensor is connected
A1 281Pump stock or running dry
E9 224Flue or high limit thermostat activated
D4 341Primary flow temperature rising too fast

Worcester Bosch GB162 Boiler Error Codes

Fault DescriptionSystem Behaviour
208The boiler is in chimney sweep mode
200The boiler is in heating mode
201The boiler is in domestic hot water (DHW) mode
202The boiler is waiting – there was a heat demand from the on off or modulating control
203The boiler is on standby
204The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature
212The temperature recorded by the flow temperature sensor or the safety sensor is rising too quickly
226Diagnosis tool was connected and is now locked out
260The flow temperature sensor is not detecting a rise in temperature following a burner start
265The boiler is waiting in response to a heat demand – the boiler regularly switches to partial load
268Component test phase
270The boiler is modulating upwards
283The boiler is preparing for a burner start – the fan and pump are activated
284The gas valve is switched
305The boiler is waiting for domestic hot water (DHW) operation to end
235The KIM (boiler identification module) is too new for the burner control unit
360The KIM that has been fitted is not compatible with the burner control unit
9A 361The burner control unit that has been fitted is not compatible with the KIM (boiler identification module)
9U 233The burner control unit or KIM (boiler identification module) is faulty
A3 317Short circuit in the flue gas temperature sensor contacts
B7 257The burner control unit or the KIM (boiler identification module) is faulty
C1 264No control signal or power supply to the fan during operation
C4 273The boiler was switched off for a maximum of 2 minutes because it had been operating continuously for more than 24 hours
C6 215The fan speed is too high
C6 216The fan speed is too low
C7 214The fan does not run during the start phase
C7 217The fan speed is irregular when starting up
CE 207Water pressure is too low
CE 266Pump test failed
D1 240The contacts of the boiler return temperature sensor have been short circuited
D1 241The contacts of the boiler return temperature sensor have been interrupted
D3 232The external switching contact has opened
D4 213The actual temperature recorded by the flow temperature sensor or return temperature sensor is rising too quickly
D4 271Actual temperature differential between flow and safety temperature sensor is too high
D4 286The boiler return temperature sensor has detected a return temperature higher than 105°c
E2 222Short circuit in the flow temperature sensor contacts
E2 223The flow temperature sensor contacts have been interrupted
E5 218The temperature captured by the flow temperature sensor exceeded 105°c
E9 210The temperature measured by the flue gas sensor is too high and is open
E9 219The safety temperature sensor has captured a temperature in excess of 105°C
E9 220The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c
E9 224The contacts of the safety temperature sensor have been interrupted
E9 276The temperature flow sensor has measured a temperature in excess of 95°c
E9 277The safety temperature sensor has measured temperature in excess of 95°c
E9 285The boiler return temperature sensor has measured a temperature higher than 95°c
E9 318The flue gas temperature sensor contacts have been interrupted
EA 227An insufficient ionisation current was measured following ignition of the burner
EA 229The ionisation current detected by the system during the burning phase was insufficient
EA 234The contacts of the gas valve have been interrupted
EA 261The burner control unit is faulty
EA 269The ignition device has been activated for too long
F0 238The burner control unit KIM (boiler identification module) is faulty
F0 239The 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.
F0 242, F0 243. F0 244.
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
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.
F0 278The sensor test has failed – cabling and plug sensors need checking
F0 279The burner control unit, or KIM, is faulty – control unit may need replacing
F0 280The burner control unit is faulty
F0 287The burner control unit, or KIM, has an error
F0 290The burner control unit, or KIM, is faulty
F7 228An ionisation current was measured before the burner started
F7 328A brief power failure has occurred
FA 306An ionisation current was measured after the burner went out
FD 231The mains voltage was interrupted during an interlocking fault
EC 256The burner control unit has an error
EH 258The burner control unit is faulty – check the plug and wiring of the burner control unit.
H07The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode
HrEThe boiler keeps resetting
rEThe boiler resets
Worcester Bosch CDI Highflow Combi Boiler Error Codes
A light on your boiler will flash to indicate that there is a fault. Depending on the type of fault, the light will flash in a different sequence.
There will be 4 quick flashes followed by a 5 second gap when the light is off and finally a series of longer flashes. The number of long flashes tells you which fault the boiler has.
Fault DescriptionSystem Behaviour
Light offNo boiler demand
Light onHeating demand on boiler is OK
1 flash 5 seconds offNo ionisation detected after ignition
2 flashes 5 seconds offLoss of ionisation signal during operation
3 flashes 5 seconds offGas valve error
4 flashes 5 seconds offFirst safety timing error / ignition timing error
5 flashes 5 seconds offIonisation 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
4 flashes 5 second gap 1 long flashSensor test failed
4 flashes, 5 second gap, 2 long flashesSafety temperature too high
4 flashes, 5 second gap, 3 long flashesMax safety thermostat activated
4 flashes, 5 second gap, 4 long flashesReturn temperature too high
4 flashes, 5 second gap, 5 long flashesFlow temperature too high – supply sensor exceeded 110°c
1 long flash, 4 quick flashes,
5 second gap, 1 long flash, 4 quick flashes
Heating control module (HCM) defective
2 long flashes, 4 quick flashes,
5 second gap, 2 long flashes, 4 quick flashes
Fan running too fast
Fan running too slow
No airflow after defined period of time
Fan not running
3 long flashes, 4 quick flashes,
5 second gap, 3 long flashes, 4 quick flashes
Mains voltage interrupted after locking error
4 long flashes, 4 quick flashes,
5 second gap, 4 long flash, 4 quick flashes
Internal control board faults
5 long flashes, 4 quick flashes,
5 second gap, 5 long flash, 4 quick flashes
All other miscellaneous faults – reset the boiler by turning the control knob anti-clockwise to the reset position
Worcester Bosch Greenstar Ri Boiler Error Codes
Fault Description​System Behaviour
No lightNo power at control board
Light onAppliance on but not operating during demand
Slow flash ( mostly off flashes on)Ignition lockout
Slow flash ( mostly on flashes off)Flue overheat or heat exchanger overheat
Fast flashVolatile lockout sensor fan or code plug
2 pulsesCheck service mode switch is in minimum position
5 pulsesCheck service mode switch is in max position
Worcester Bosch Error Code EA 229 or D5

If you’re seeing the error code EA 229 or D5 on your Worcester Bosch boiler, this means that the condensate pipe is frozen.
This happens due to the condensate pipe running outside, however this is an issue that you could fix yourself if you feel confident enough, you can find out how in our handy guide.

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