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

Worcester Bosch Greenstar CDi Classic Combi Fault 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 Fault 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 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
H07   Water pressure too low
HrE   Boiler keeps resetting
rE   Boiler resets