Worcester Bosch Boiler Fault Codes Guide

Posted on 22nd January 2021 by H2 Property Services

Is your Worcester-Bosch boiler displaying seemingly random letters and numbers? These are known as ‘fault codes’ or ‘error codes’.

These codes appear when your boiler has experienced a fault, with each code representing a specific issue. You may be able to resolve some issues yourself, or you may need professional intervention from an experienced boiler engineer. Use this guide to find out your next steps to fixing your Worcester-Bosch boiler.

Worcester Bosch Boiler Fault Codes

If you need boiler services across London, use a boiler engineer that you can trust. H2 Property Services have been fixing boilers for over 15 years. All our engineers are gas-safe certified and can fix boilers from all the leading manufacturers. Using your boiler’s fault code and our wealth of experience, we will locate and fix any problems quickly. We even offer emergency call-outs if your boiler needs immediate attention. Simply get in touch and we’ll be there.

For trusted boiler services in London, give our team a call today on 020 7751 3344. Or use our quick quote form!

Find your Worcester Bosch Boiler Model:

• CDI Classic Comb
• CDI Highflow Comb
• CDi Compact
• CDi Classic Regular
• Greenstar I System / Combi
• GB162
• CDI Highflow Combi
• Greenstar Ri
• Greenstar 8000
• Error Code EA 229 or D5

 

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Worcester Bosch CDI Classic Combi Boiler Error Codes

 

Fault Code	Reason(s)
A1	Water is leaking or the pump needs replacing or freeing due to the pump running dry.
A7	The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads need checking.
A8	Break communication to FX sensor controls electrical connections need checking.
B1	Code plug not detected .
C6	Fan speed too low – the fan lead and connector need checking and may need replacing.
E2	Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.
E9	Safety temperature limiter in central heating (CH) flow has tripped the system pressure or safety temperature limiter needs checking
EA	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.
F0	Internal error – electrical connector contacts or programmer interface module – check ignition leads are not loose.
F7	Flame detected even though the appliance is switched off – check the electrode assembly is dry and the pcb and flue are clear.
FA	Flame detected after gas shut off – the gas valve needs checking – hire a Gas Safe installer.
FD	Reset button pressed by mistake – press reset button again.

 

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Worcester Bosch CDI Highflow Combi Boiler Error Codes

 

Fault Code	Reason(s)
A1	Pump dry run detection or pump is running in air the system pressure needs checking
A5	Tank negative thermistor coefficient (NTC) defect
A7	Domestic hot water (DHW) negative thermistor coefficient (NTC) defect
A8	Energy Management System (EMS) communication error
B1	Code plug not detected
B2, B3, B4, B5, B6	Data error
B7	Burner control error
C6	Fan defect
D3	External temperature limiter
D5	Condensate pump failure
D6	Internal heat bank overflow
EA	Flame not detected
E2	Primary negative thermistor coefficient (NTC) defect
E9	Safety temperature limiter in central heating (CH) flow stat tripped
F0	Internal error
F1	ROM fault
F7	Flame detected after appliance has been shut off
FA	Flame detected after gas shut off
FD	Reset button pressed – try pressing the reset button again

 

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

 

Fault Code	Reason(s)
T1	Ignition test – checking the igniter spark
T2	Fan test – checking the basic fan
T3	Pump test – checking the basic pump
T4	Three way valve test
T6	Ionisation oscillator test
9A 362	error – incorrect HCM fitted
9U 233	Heat Control Module (HCM) error – problem with code plug
B7 257	Internal error – possible control board problem
C6 215	Fan problem – fan running too fast
C7 214	Fan problem – fan not running
D1 240	Return sensor error – sensor may be wet or damaged
E2 222	Flow sensor short circuit error
E5 218	Flow temperature too high
E9 219	Safety sensor fault – temperature too high, sensor short circuit or open circuit
EA 227	No flame detected or flame signal loss during operation
F0 237	Internal error
F7 228	Flame error – false flame or flame detected before burner started
FA 306	False flame fault – flame detected after burner stop
FD 231	Mains power fault – electrical power interruption
FA 364	Gas valve EV2 leak test failed – gas valve leak
FB 365	Gas valve EV1 leak test failed
A1 281	Pump stuck or running with air in the system
C1 264	Airflow stopped during operation
C4 273	Airflow present during last 24 hour
D1 240	Return sensor short circuit
D4 271	Temperature difference between flow and safety sensor exceeds limit
E9 224	Max thermostat activated – flue gas thermostat overheat
EA 227	No ionisation detected after ignition
EF 349	Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212	Safety or flow temperature rising too fast

 

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Worcester Bosch CDi Classic Regular Boiler Error Codes

 

Fault Code	Reason(s)
B1	Code plug not detected
C6	Fan speed too low
E2	Central heating (CH) flow negative thermistor coefficient (NTC) sensor defective
E9	Safety temperature limiter in central heating (CH) flow has tripped
EA	Flame not detected
F0	Internal error
F7	Flame detected even though appliance switched off
FA	Flame detected after gas shut off
FD	Reset button pressed by mistake

 

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Worcester Bosch Greenstar I System / Combi Boiler Error Codes

 

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

 

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Worcester Bosch GB162 Boiler Error Codes

 

Fault Codes	Reason(s)
208	The boiler is in chimney sweep mode
200	The boiler is in heating mode
201	The boiler is in domestic hot water (DHW) mode
202	The boiler is waiting – there was a heat demand from the on off or modulating control
203	The boiler is on standby
204	The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature
212	The temperature recorded by the flow temperature sensor or the safety sensor is rising too quickly
226	Diagnosis tool was connected and is now locked out
260	The flow temperature sensor is not detecting a rise in temperature following a burner start
265	The boiler is waiting in response to a heat demand – the boiler regularly switches to partial load
268	Component test phase
270	The boiler is modulating upwards
283	The boiler is preparing for a burner start – the fan and pump are activated
284	The gas valve is switched
305	The boiler is waiting for domestic hot water (DHW) operation to end
235	The KIM (boiler identification module) is too new for the burner control unit
360	The KIM that has been fitted is not compatible with the burner control unit
9A 361	The burner control unit that has been fitted is not compatible with the KIM (boiler identification module)
9U 233	The burner control unit or KIM (boiler identification module) is faulty
A3 317	Short circuit in the flue gas temperature sensor contacts
B7 257	The burner control unit or the KIM (boiler identification module) is faulty
C1 264	No control signal or power supply to the fan during operation
C4 273	The boiler was switched off for a maximum of 2 minutes because it had been operating continuously for more than 24 hours
C6 215	The fan speed is too high
C6 216	The fan speed is too low
C7 214	The fan does not run during the start phase
C7 217	The fan speed is irregular when starting up
CE 207	Water pressure is too low
CE 266	Pump test failed
D1 240	The contacts of the boiler return temperature sensor have been short circuited
D1 241	The contacts of the boiler return temperature sensor have been interrupted
D3 232	The external switching contact has opened
D4 213	The actual temperature recorded by the flow temperature sensor or return temperature sensor is rising too quickly
D4 271	Actual temperature differential between flow and safety temperature sensor is too high
D4 286	The boiler return temperature sensor has detected a return temperature higher than 105°c
E2 222	Short circuit in the flow temperature sensor contacts
E2 223	The flow temperature sensor contacts have been interrupted
E5 218	The temperature captured by the flow temperature sensor exceeded 105°c
E9 210	The temperature measured by the flue gas sensor is too high and is open
E9 219	The safety temperature sensor has captured a temperature in excess of 105°C
E9 220	The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c
E9 224	The contacts of the safety temperature sensor have been interrupted
E9 276	The temperature flow sensor has measured a temperature in excess of 95°c
E9 277	The safety temperature sensor has measured temperature in excess of 95°c
E9 285	The boiler return temperature sensor has measured a temperature higher than 95°c
E9 318	The flue gas temperature sensor contacts have been interrupted
EA 227	An insufficient ionisation current was measured following ignition of the burner
EA 229	The ionisation current detected by the system during the burning phase was insufficient
EA 234	The contacts of the gas valve have been interrupted
EA 261	The burner control unit is faulty
EA 269	The ignition device has been activated for too long
F0 238	The burner control unit KIM (boiler identification module) is faulty
F0 239	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.
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 278	The sensor test has failed – cabling and plug sensors need checking
F0 279	The burner control unit, or KIM, is faulty – control unit may need replacing
F0 280	The burner control unit is faulty
F0 287	The burner control unit, or KIM, has an error
F0 290	The burner control unit, or KIM, is faulty
F7 228	An ionisation current was measured before the burner started
F7 328	A brief power failure has occurred
FA 306	An ionisation current was measured after the burner went out
FD 231	The mains voltage was interrupted during an interlocking fault
EC 256	The burner control unit has an error
EH 258	The burner control unit is faulty – check the plug and wiring of the burner control unit.
H07	The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode
HrE	The boiler keeps resetting
rE	The boiler resets

 

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Worcester Bosch CDI Highflow Combi Boiler Error Codes

 

Fault Code	Reason(s)
Light off	No boiler demand
Light on	Heating demand on boiler is OK
1 flash 5 seconds off	No ionisation detected after ignition
2 flashes 5 seconds off	Loss of ionisation signal during operation
3 flashes 5 seconds off	Gas valve error
4 flashes 5 seconds off	First safety timing error / ignition timing error
5 flashes 5 seconds off	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
4 flashes 5 second gap 1 long flash	Sensor test failed
4 flashes, 5 second gap, 2 long flashes	Safety temperature too high
4 flashes, 5 second gap, 3 long flashes	Max safety thermostat activated
4 flashes, 5 second gap, 4 long flashes	Return temperature too high
4 flashes, 5 second gap, 5 long flashes	Flow 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

 

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Worcester Bosch Greenstar Ri Boiler Error Codes

 

Fault Code	Reason(s)
No light	No power at control board
Light on	Appliance 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 flash	Volatile lockout sensor fan or code plug
2 pulses	Check service mode switch is in minimum position
5 pulses	Check service mode switch is in max position

 

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Worcester Bosch Greenstar 8000 Boiler Error Codes

 

Fault Code	Reason(s)
200 O	Boiler in heating mode
201 O	Boiler in hot water mode
202 O	Boiler in anti-cycle mode
203 0	Boiler in standby – no heat energy demand
204 O	Current primary water temperature higher than set value
208 0	Chimney sweep demand
224 V	Safety temperature limiter has tripped – top-up water until the reset pressure is reached
227 V	No flame signal after ignition burner control unit could need replacing
228 V	Flame signal without flame present – air/gas ratio control valve may need replacing as might the ionisation cable
305 0	Boiler in hot water anti-cycle mode
306 V	Flame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
360 V	Incompatible code plug – check if a correct code plug is installed and exchange or reconnect code plug
815 W/B	Low loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage
1010 O	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
1017 W	Water pressure too low – the water needs topping up and the vent system or pressure sensor may need replacing
1021 B	Hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected
1022 B	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
1037 W	Outside temperature sensor is defective – check the connecting lead
1065 B	Pressure sensor defective or not connected – check pressure sensor connection as it may need replacing
1068 W	Outside temperature sensor defective – check the connecting lead
1073 W	Short circuit of the flow temperature sensor – the temperature sensor may need replacing
1074 W	No signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or temperature sensor could need replacing
1075 W	Short circuit of the temperature sensor at the heating block – temperature sensor may need replacing
1076 W	No signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead or the control unit
2920 V	Error with the flame monitoring
2924 V	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
2925 V	Feedback from the modulating gas valve is too low
2927 B	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
2946 V	Incorrect code plug detected – the code plug needs replacing
2948 B	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
2950 B	No flame signal. Following starting procedure the burner starts automatically. After cleaning set the correct gas / air ratio correctly
2963 B	Signal from flow and heat exchanger temperature sensor outside the permissible range – the connecting lead needs connecting correctly
2964 B	Flow rate in heat exchanger is too low
2965 B	Flow temperature too high
2966 B	Flow temperature rise in heat exchanger too rapid
2967 B	Flow / heat exchanger temperature sensor differential too great
2970 B	Pressure drop in heating system too rapid
2971 B	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

 

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.

 

Worcester Bosch Boiler Engineers London

Our knowledge and exposure to all the different makes and models means that they are quickly able to diagnose faults and correctly identify parts for replacement. Our specialists can also make long-lasting repairs and carry out effective maintenance services.

This helps to ensure the length-of-life of your boiler is extended as long as possible. This allows us to pass on to our customers extended warranties of up to 8 years for their new boilers. We are experienced with all makes and models of boilers, and our friendly team are always happy to help.

Contact our team today on 020 7751 3344 for a quote.

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