Worcester Bosch Boiler Issues: Errors and Fault Codes
When your Worcester Bosch boiler starts to play up, it can be difficult to know whether the fault is simple to fix or whether it’s a serious issue that requires urgent attention from an engineer. The majority of the time, your Worcester Bosch boiler will shut down or display a unique fault code or an error message to let you know that something isn’t right. Fault codes are designed to make it easy for your engineer to identify the possible cause of a fault, and you may be asked for the code when you call an engineer for assistance.
Your Worcester Bosch boiler manual should list the fault codes and error codes that could appear on your boiler. If you have misplaced your manual and your boiler is displaying a fault code, you can search through our tables below to find out what the error message means.
Worcester Bosch Boiler Fault Codes by Type
Fault Description
Codes That Will Appear On Your Boiler
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 Locking Error Codes
Fault Code
Cause Code
Possible Cause
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
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
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 Fault 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 Fault 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 Fault 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 control signal or power supply to 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
[1] British Gas acts as a credit broker, not the lender and offers products from a panel of lenders. Payment options are subject to change without notice. British Gas is a trading name of British Gas New Heating Limited (No. 06723244), an appointed representative of British Gas Services Limited (No. 03141243) which is authorised and regulated by the Financial Conduct Authority (Financial Services Register No. 490568). Both companies registered in England and Wales. Registered office: Millstream, Maidenhead Road, Windsor, Berkshire SL4 5GD. Availability of credit depends on status and credit checks. Terms and Exclusions apply.
[2] £100 additional discount is only available to British Gas energy and British Gas HomeCare 1-4 customers who choose to have a British Gas installation. This offer is available to homeowners and landlords with a total system output of up to 50kW who already have a British Gas energy tariff or HomeCare 1-4 at the property where the boiler would be installed. Available to 98% of UK mainland households. This offer cannot be used by tenants, British Gas multi–premise landlord customers and cannot be used in conjunction with staff/ex-staff/partner discounts. Terms and Exclusions apply. Offers are subject to change without notice.
[3] Saving when upgrading from a G-rated boiler to an A-rated boiler in a detached home using the average energy bill for a high usage house. Source: http://www.energysavingtrust.org.uk/home-energy-efficiency/boiler-replacement and https://www.britishgas.co.uk/energy/guides/average-bill.html
British Gas is a trading name of British Gas New Heating Limited (No. 06723244), an appointed representative of British Gas Services Limited (No. 03141243) which is authorised and regulated by the Financial Conduct Authority (Financial Services Register No. 490568). Both companies registered in England and Wales. Registered office: Millstream, Maidenhead Road, Windsor, Berkshire SL4 5GD. Availability of credit depends on status and credit checks. Terms and Exclusions apply. Saving when upgrading from a G-rated boiler. Source: http://www.energysavingtrust.org.uk/home-energy-efficiency/boiler-replacement
