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 |
Borken Worcester Bosch? Get a new Worcester boiler quote here
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.
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