Worcester Bosch Boiler Issues, Errors, and Fault Codes

When a Worcester Bosch boiler starts not to run as it should, it can be frustrating not knowing whether the fault is for you to fix or if it’s an issue that requires attention from a Gas Safe engineer, or a new boiler.

More often than not, the Worcester Bosch boiler will close down, or on display, a fault code, or an error message will show.

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What are Worcester fault codes?

Fault codes are used to code, so it is simple for a Gas Safe engineer to pinpoint the cause of the issue. You could be asked for the code which is showing on the display when you call the Gas Safe engineer.

The Worcester Bosch manufacturer manual should list the fault codes and error codes that may show up on your boiler display.

If you cannot find the manufacturer manual which came with your boiler and your boiler is showing a fault code, you can look through the information below to find out what the error code stands for.

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Worcester Bosch Fault Codes:

FAULT DESCRIPTION	CODES THAT WILL APPEAR ON YOUR BOILER DISPLAY:
Blocking Error	The boiler will stop operating but no fault code will appear. You can access the cause code by pressing the spanner/return button. The condition will clear once the fault clears. For instance, if the boiler is waiting for an area to cool, the error will clear automatically once the associated area has cooled down.
Locking Error	The boiler will flash a warning triangle and a fault code. It will also show a static cause code. You’ll need to press the boiler reset button to clear the code, but only after the boiler has been fixed.
Fault Error	The boiler will display an alphanumeric fault code to indicate the fault group.
Cause Error	A three-digit number that can be accessed via the info menu by pressing the spanner/return button during a blocking error or when in normal operating status. The cause code should flash on the display during a locking error.
Maintenance Code	A maintenance code is displayed with the letter H followed by a number. The fault won’t stop the boiler from working but it tells you that the boiler needs to be looked at by a qualified engineer.

Worcester Bosch Boiler Shut Down Error Codes:

FAULT CODE	CAUSE CODE	POSSIBLE ISSUE:
9A	362	Incorrect Heat Control Module (HCM) has been fitted
9U	233	Code plug is faulty or not connected
B7	257	Need to replace control board
C6	215	Fan running too fast
C6	216	Fan running too slow
C7	214	Fan not running at all
C7	217	Fan not running or the airflow is blocked
D1	240	Sensor wet or damaged – the boiler will usually block for 300 seconds before the fault code is displayed
D1	241	Sensor is disconnected or damaged – the boiler will usually block for 300 seconds before the fault code is displayed
D1	286	Boiler overheating
E2	222	Flow sensor shorted or damaged
E2	223	Flow sensor damaged or disconnected
E5	218 or 332	Primary flow sensor overheated
E9	219	Main heat exchanger overheated
E9	220	Maximum temperature sensor on main heat exchanger has failed
E9	221	Maximum temperature sensor on main heat exchanger not recognised
E9	224	Flue gas thermostat overheated
EA	227	Failure of four ignition attempts – Need to wait at least 30 seconds before another attempt is made
EA	229	Established flame has been extinguished – Could be caused by a blocked sump or strong wind into the flue
EA	234	Gas valve coil disconnected
EA	261	No flame established during the first 4 seconds of ignition period
EA	338	Pump not detecting water – check pressure gauge and re-pressurise to 1 bar

Worcester Bosch Boiler Blocking Fault Codes:

FAULT CODE	CAUSE CODE	POSSIBLE CAUSE
A1	281	Low or no water in the system – check pressure gauge and re-pressurise to 1 bar
C1	264	Fan stopped working
EA	227	No flame detected – boiler will block during 4 attempts before going to a locking fault
EF	349	Boiler operating at minimum burner load and there is a greater flow and return temperature than 18°C
No code	212 or 213	Airlock or reduced water content – check pressure gauge and re-pressurise to 1 bar
No code	260	Sensor disconnected or no water content – check pressure gauge and re-pressurise to 1 bar

Worcester Bosch 4000 error codes

Error codes for the new Worcester Bosch 4000 boilers

faulterror Code	Error Meaning
Code: 1021	Cylinder charging or hot water temperature sensor faulty. The hot water sensor has been changed if an open or short circuit or refitted to the pipe if it has fallen off. Turn the appliance off and back on again.
Code: 224	Arrange a visit from a Worcester Bosch engineer to reset the boiler/PCB. This is a software issue.

Worcester Bosch Greenstar CDi Classic Combi Error Codes:

Greenstar CDi Classic combi boiler error codes

FAULT CODE	DESCRIPTION
A7	Hot water NTC sensor defective
A8	Break in communication to FX controls
b1	Code plug not detected
C6	Fan speed too low
E2	CH flow NTC sensor defective
E9	Safety temperature limiter in CH flow has tripped
EA	Flame not detected. If safe, check that the gas is on in the house OR check for a frozen condensate pipe. Could be a blocked flue outlet – contact a Gas Safe engineer
F0	Internal error
F7	Flame detected even though boiler is switched off
FA	Flame detected after the gas has been shut off
Fd	Reset button pressed by mistake

Worcester Bosch Greenstar CDi Highflow Combi Error Codes:

FAULT CODE	DESCRIPTION
A7	Hot water NTC sensor defective
A8	Break in communication to weather compensating clip-in control of Greenstar Comfort II RF
B1	Code plug not detected
C6	Fan speed too low
D5	Condensate pipe fault
E2	CH flow NTC sensor defective
E9	Safety temperature limiter in CH flow has tripped
EA	Flame not detected. If safe, check that the gas is on in the house OR check for a frozen condensate pipe. Could be a blocked flue outlet – contact a Gas Safe engineer
F0	Internal error
F7	Flame detected even though boiler is switched off
FA	Flame detected after gas shut off
Fd	Reset button pressed by mistake
SE	Service required
U1, U2 or U3	Boiler flow temperature is too high and the boiler will shut down until it has cooled down

Worcester Greenstar Heatslave II Oil Combi Error Codes:

FAULT CODE	CAUSE CODE	DESCRIPTION
E9	210	Maximum temperature thermostat or air pressure witch activated. Reset overheat thermostat or air pressure switch before resetting boiler
E5	218	Flow temperature too high
E9	219, 220 or 221	Safety temperature too high, safety sensor short circuit or safety sensor open circuit
E2	222, 223 or 233	Flow sensor short circuit, flow sensor open circuit or heat control module code plug missing or defective
F0	237 or 238	Software relay error – Resistors between plus X4 pins 3 & 5 disconnected or water in the burner control box
F0	239 or 259	Watchdog relay error or A/D reference relay error – If error persists, change the control board
F0	263	Appliance powered off with locking fault present – press reset button to clear
D4	271	Temperature difference between flow and safety sensors exceeds the limit
E9	276 or 277	Flow temperature or safety temperature exceeds 95°C
F0	278, 279 or 290	Sensor test error, A/D convertor error or A/D convertor reference error
E5	332	Primary flow has exceeded 105°C – primary sensor overheated
9A	360	Incorrect HCM for boiler variant – replace with correct HCM
A7	808	DHW sensor defective – check and replace defect sensor as necessary
A0	809	Thermal store sensor defective – check and replace defect sensor as necessary
9F	855 or 856	Burner lockout or 5 burner lockouts repeated resets. Check the burner and fuel supply, and ensure oil supply is free of contaminants. After five 855 burner lockouts, code 856 is displayed.
H29	N/A	Warning triangle and house symbol displayed on controller – weather compensation activated but no weather sensor detected. Refer to section 5.11 on page 32 of manual
H27	N/A	Warning triangle symbol displayed on controller – DCW in sensor defect

Worcester Bosch Greenstar CDi Classic System Error Codes:

FAULT CODE	DESCRIPTION
b1	Code plug not detected
C6	Fan speed too low
E9	Safety temperature limiter in CH flow has tripped
EA	Flame not detected. If safe, check that the gas is on in the house OR check for a frozen condensate pipe. Could be a blocked flue outlet – contact a Gas Safe engineer
F0	Internal error
F7	Flame detected even though boiler is switched off
FA	Flame detected after gas shut off
Fd	Reset button pressed by mistake

Worcester Bosch GB162 System Error Codes:

FAULT CODE	CAUSE CODE	DESCRIPTION
N/A	208	Boiler is in chimney sweep mode
N/A	200	Boiler is in heating mode
N/A	201	Boiler is in domestic hot water mode
N/A	202	Boiler is waiting because there is a heat demand from the on/off or modulating control
N/A	203	Boiler is on standby
N/A	204	Boiler is waiting because the actual temperature is higher than the calculated or selected temperature
N/A	212	The temperature recorded by the flow temperature sensor or safety sensor is rising too fast
N/A	226	Diagnoses tool was connected and is now locked out
N/A	260	The flow temperature sensor is not detecting a rise in temperature after a burner start
N/A	265	Boiler is waiting in response to a heat demand – boiler regularly switches to partial load
N/A	268	Component test phase
N/A	270	Boiler is modulating upwards
N/A	283	Boiler is preparing for a burner start – fan and pump activated
N/A	284	Gas valve is switched on
N/A	305	Boiler is waiting for domestic hot water operation to finish
N/A	235	The KIM (boiler identification module) is too new for burner control unit
N/A	360	The fitted KIM is not compatible with the burner control unit
9A	361	The fitted burner control unit is not compatible with the KIM
9U	233	The burner control unit or KIM is faulty
A3	317	Short circuit in the flue gas temperature sensor contacts
B7	257	Burner control unit or KIM is faulty
C1	264	No power or control signal to supply the fan
C4	276	Boiler switched off for a max of 2 minutes because it has been operating non-stop for 24 hours
C6	215	Fan speed too high
C6	216	Fan speed too low
C7	214	Fan doesn’t run during start phase
C7	217	Fan speed is irregular on start up
CE	207	Water pressure too low
CE	266	Pump test failed
D1	240	Interruption to contacts of boiler return temperature sensor
D3	232	External switching contact is open
D4	213	Temperature recorded by the flow temperature sensor or return temperature sensor is rising too fast
D4	271	Temperature differential between flow and safety temperature sensor is too high
D4	286	Boiler return temperature sensor has detected a return temperature higher than 105°C
E2	222	Short circuit in flow temperature sensor contacts
E2	223	Interruption to flow temperature sensor contacts
E5	218	Temperature sensed by flow temperature sensor is higher than 105°C
E9	210	Temperature measured by flue gas sensor is open and too high
E9	219	Safety temperature sensor has sensed a temperature higher than 105°C
E9	220	Contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature that exceeds 105°C
E9	224	Interruption to the safety temperature sensor
E9	276	Temperature flow sensor has sensed a temperature higher than 95°C
E9	277	Safety temperature sensor has sensed a temperature higher than 95°C
E9	285	Boiler temperature sensor has sensed a temperature higher than 95°C
E9	318	Interruption to flue gas sensor contacts
EA	227	Insufficient ionisation current measured following ignition of burner
EA	229	Insufficient ionisation current detected by system during the burning phase
EA	234	Interruption to contact of the gas valve
EA	261	Faulty burner control unit
EA	269	Ignition device activated for too long
F0	238	Faulty burner control unit (KIM)
F0	239	Error with burner control unit (KIM)
F0	242 to 253 and 255, 259, 263, 267 and 272	Faulty burner control unit (KIM)
F0	278	Sensor test failed – check cabling and plug sensors
F0	279	Faulty burner control unit or KIM – may need to replace control unit
F0	280	Faulty burner control unit
F0	287	Error with burner control unit or KIM
F0	290	Faulty burner control unit or KIM
F7	228	Ionisation current measured before burner started
F7	328	Power failure occurred
FA	306	Ionisation current measured after burner went out
FD	231	Interruption to mains voltage during interlocking fault
EC	256	Burner control unit error
EH	258	Faulty burner control unit – check plug and wiring
H07		Water pressure too low
HrE		Boiler keeps resetting
rE		Boiler resets

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Hopefully, our guide has helped you figure out what the issue is. If you need more help, try the Worcester Bosch site. If you need a new boiler and want to find out how much new boiler costs, however, we can help you get a brand new boiler installed tomorrow, all at a fixed price.