WB
Worcester Bosch Fault Codes
Select a fault code to see its meaning, common causes and how to fix it.
Greenstar CDi, i, Si & Compact fault codes
- 9A The 9A fault code — displayed alongside cause code 362 — tells you that the boiler's Heat Control Module (HCM) is… Read more →
- 9A 362 The 9A 362 fault code indicates that the boiler's Heat Control Module (HCM) is not correctly matched to the appliance.… Read more →
- 9U The 9U fault code on Worcester Bosch boilers is a locking error that points to a problem with the Heat Control Module… Read more →
- 9U 233 The 9U 233 fault code points to a problem with the code plug inside the Heat Control Module (HCM) — the electronic… Read more →
- A1 The A1 fault code on a Worcester Bosch boiler indicates that the circulation pump is not performing as the boiler… Read more →
- A1 281 The A1 fault code on Worcester Bosch boilers signals that the central heating pump has encountered a problem — most… Read more →
- A3 The A3 code is a locking fault that appears when the boiler detects a problem with its fan or the air pressure switch… Read more →
- A3 317 The A3 317 code indicates that the boiler's control system has detected a short circuit in the flue gas temperature… Read more →
- A7 The A7 fault code indicates that your Worcester Bosch boiler has detected a problem with the domestic hot water (DHW)… Read more →
- A8 The A8 fault code means your Worcester Bosch boiler has lost communication with its FX sensor controls or programmer.… Read more →
- A8 362 The A8 362 fault code has two layers. The primary code — A8 — tells you the boiler's Energy Management System (EMS) has… Read more →
- B1 The B1 fault code means your Worcester Bosch boiler has lost communication with its code plug — a small but essential… Read more →
- B7 The B7 fault code — almost always displayed alongside cause code 257 on Worcester Bosch boilers — signals that the… Read more →
- B7 257 The B7 257 fault code indicates an internal electrical error within the boiler. Specifically, the boiler's onboard… Read more →
- C1 The C1 fault code on Worcester Bosch boilers — most commonly displayed as C1 264 on Greenstar i, Si, CDi, and Greenstar… Read more →
- C1 264 The C1 264 fault code means the boiler's fan stopped running while the appliance was mid-cycle. Unlike fault codes that… Read more →
- C4 The C4 fault code indicates that Worcester Bosch's boiler control system has detected a problem with the fan or the way… Read more →
- C4 237 The C4 fault code on Worcester Bosch boilers signals a fan or airflow anomaly — the boiler's controls have detected… Read more →
- C4 273 The C4 273 fault code indicates that your Worcester Bosch boiler has detected continuous fan or airflow activity over… Read more →
- C6 The C6 fault code appears on Worcester Bosch boilers when the control system detects that the flue fan is either not… Read more →
- C6 215 The C6 fault family on Worcester Bosch boilers relates to the flue fan, and sub-code 215 specifically indicates that… Read more →
- C6 216 The C6 216 code means your Worcester Bosch boiler has detected that its fan is spinning more slowly than it should be.… Read more →
- C7 The C7 fault code appears when the boiler's fan fails to reach the correct operating speed — or fails to start at all —… Read more →
- C7 214 The C7 214 fault code tells you that the boiler's fan failed to reach the correct speed — or didn't turn at all —… Read more →
- C7 216 Worcester Bosch boilers use a two-part fault code system: the letter-number prefix (C7) identifies the fault category,… Read more →
- C7 217 The C7 217 fault code appears when the boiler detects that the fan has stopped or behaved erratically during normal… Read more →
- CC The CC fault code on a Worcester Bosch boiler signals a problem with the outdoor temperature sensor — specifically an… Read more →
- CC 800 The CC fault code (displayed as CC 800 on some Worcester Bosch models) indicates a problem with the optional outdoor… Read more →
- CE The CE fault code on a Worcester Bosch boiler most commonly signals that the system water pressure has dropped below… Read more →
- CE 207 The CE 207 fault code on Worcester Bosch boilers is one of those codes where the underlying cause depends heavily on… Read more →
- CE 266 The CE 266 code appears on Worcester Bosch boilers when the control system has detected an abnormality with the central… Read more →
- D1 The D1 fault code appears when your Worcester Bosch boiler is unhappy with the reading coming from its return NTC… Read more →
- D1 240 The D1 fault code on a Worcester Bosch boiler points to a problem with the return NTC thermistor — the temperature… Read more →
- D1 241 The D1 fault code on Worcester Bosch boilers relates to a problem with the return NTC thermistor — the temperature… Read more →
- D3 The D3 fault code indicates that the boiler's external temperature limiter has tripped or there is a fault with the PCB… Read more →
- D3 232 The D3 fault code on a Worcester Bosch boiler means the boiler has locked out because an external switching contact has… Read more →
- D4 The D4 fault code means your Worcester Bosch boiler has detected that the primary flow temperature is climbing more… Read more →
- D4 213 The D4 213 fault code indicates that the boiler has detected its flow or return water temperature climbing too rapidly… Read more →
- D4 271 The D4 271 fault code means the boiler has detected an excessive temperature difference between the primary flow sensor… Read more →
- D4 286 The D4 286 fault code tells you that the boiler's return NTC thermistor — the sensor monitoring the temperature of… Read more →
- D4 341 The D4 341 fault code appears on Worcester Bosch Greenstar boilers when the primary flow temperature is climbing too… Read more →
- D5 The D5 code on a Worcester Bosch boiler does not have a single universal meaning — its interpretation depends on which… Read more →
- E2 The E2 fault code on a Worcester Bosch boiler indicates that the central heating flow temperature NTC (Negative… Read more →
- E2 222 The E2 222 code tells you that the boiler's central heating flow NTC (Negative Temperature Coefficient) temperature… Read more →
- E2 223 The E2 fault code on Worcester Bosch boilers points to a problem with the flow temperature NTC (Negative Temperature… Read more →
- E2 233 The E2 fault code signals that your boiler has detected a problem with the central heating (CH) flow NTC temperature… Read more →
- E2 350 The E2 code on a Worcester Bosch boiler points to a locking fault with the flow temperature NTC (Negative Temperature… Read more →
- E2 351 The E2 351 fault code on a Worcester Bosch boiler tells you that the central heating flow NTC (Negative Temperature… Read more →
- E5 The E5 fault code on a Worcester Bosch boiler points to a problem with the flow temperature sensor — the component that… Read more →
- E5 218 The E5 218 fault code indicates that the boiler's flow temperature has exceeded safe operating limits — specifically,… Read more →
- E9 The E9 fault code means the safety temperature limiter on your central heating flow circuit has tripped. Your boiler… Read more →
- E9 210 The E9 fault code signals that the boiler's safety temperature limiter in the central heating flow has tripped, forcing… Read more →
- E9 219 The E9 fault code on a Worcester Bosch boiler means the safety temperature limiter in the central heating flow has… Read more →
- E9 220 The E9 code means the boiler's safety temperature limiter has tripped after detecting that water in the central heating… Read more →
- E9 224 The E9 fault on Worcester Bosch boilers indicates that the safety temperature limiter has tripped because the central… Read more →
- E9 276 The E9 fault code indicates that the safety temperature limiter in your central heating flow circuit has tripped. The… Read more →
- E9 277 The E9 fault code on Worcester Bosch boilers means the safety temperature limiter in the central heating flow circuit… Read more →
- E9 285 The E9 fault code on a Worcester Bosch boiler means the central heating safety temperature limiter has tripped. The… Read more →
- E9 318 The E9 fault code appears on Worcester Bosch boilers when the central heating flow temperature has exceeded its safe… Read more →
- EA The EA fault code on a Worcester Bosch boiler means the appliance has tried to light its burner — typically up to four… Read more →
- EA 227 The EA 227 fault code means your Worcester Bosch boiler attempted to light the burner, failed to detect a flame through… Read more →
- EA 229 The EA 229 fault code means your Worcester Bosch boiler established a flame successfully but then lost it while… Read more →
- EA 234 The EA 234 fault code on a Worcester Bosch boiler sits within the broader EA fault family, which covers flame detection… Read more →
- EA 261 The EA 261 code tells you that your Worcester Bosch boiler has locked out after failing to establish or confirm a… Read more →
- EA 269 The EA fault code on a Worcester Bosch boiler means the boiler has failed to detect a stable flame after multiple… Read more →
- EC If your Worcester Bosch boiler is showing what looks like an 'EC' fault code, it is almost certainly displaying 'EA' —… Read more →
- EC 256 On Worcester Bosch boilers, 256 is a cause code — a three-digit secondary diagnostic number that appears alongside a… Read more →
- EF The EF fault code — typically displayed alongside cause code 349 — indicates that your Worcester Bosch boiler has… Read more →
- EF 349 The EF 349 fault code means the boiler has detected a 'central heating boil' condition — specifically, the temperature… Read more →
- EH The EH fault code — most commonly displayed as EH 258 — tells you that the boiler's Heat Control Module (HCM) has been… Read more →
- EH 258 EH 258 indicates an internal fault within the boiler's heat and burner control electronics. On Greenstar i Combi… Read more →
- F0 The F0 fault code signals that your Worcester Bosch boiler has detected a serious internal error and has stopped normal… Read more →
- F0 237 The F0 237 code indicates that your Worcester Bosch boiler has detected an internal fault within its control… Read more →
- F0 238 The F0 prefix on a Worcester Bosch boiler signals an internal component failure that has caused the boiler to lock out… Read more →
- F0 239 The F0 239 fault code on a Worcester Bosch boiler signals an internal error within the Burner Control Unit, also known… Read more →
- F0 242 The F0 242 fault code on a Worcester Bosch boiler signals a problem with the burner control unit — known as the KIM.… Read more →
- F0 258 The F0 258 fault code on a Worcester Bosch boiler has two parts that together pinpoint the problem. The F0 prefix… Read more →
- F0 262 The F0 262 fault code is a locking error, meaning your Worcester Bosch boiler has shut itself down completely and will… Read more →
- F0 272 The F0 272 code appears on Worcester Bosch Greenstar i combi boilers and indicates a problem with the Burner Control… Read more →
- F0 278 The F0 prefix on a Worcester Bosch boiler signals a general internal lockout caused by a failure within the appliance's… Read more →
- F0 279 The F0 279 code tells you that your Worcester Bosch boiler has detected a fault specifically with the burner control… Read more →
- F0 280 The F0 fault family on Worcester Bosch boilers signals an internal component or control system failure. When your… Read more →
- F0 287 The F0 fault code on Worcester Bosch boilers signals an internal component failure detected by the boiler's control… Read more →
- F0 290 The F0 290 fault code indicates that the boiler's internal control electronics have detected a problem with the Heat… Read more →
- F1 The F1 fault code on a Worcester Bosch boiler signals an ignition failure — the boiler has tried to light and been… Read more →
- F1 259 The F1 259 code tells you that the boiler's internal electronics have detected a problem with the Heat Control Module… Read more →
- F1 263 The F1 263 fault code is a locking error on Worcester Bosch boilers that points to a problem with the Heat Control… Read more →
- F7 The F7 fault code means your Worcester Bosch boiler's ionisation circuit has detected a flame signal at a point when… Read more →
- F7 228 The F7 228 fault code means the boiler's ionisation (flame) sensor detected an electrical signal consistent with a… Read more →
- F7 328 The F7 fault code means your Worcester Bosch boiler has detected an ionisation signal — in other words, it thinks a… Read more →
- FA The FA fault code means your Worcester Bosch boiler has detected a flame signal at a point when the gas valve should be… Read more →
- FA 306 The FA 306 fault code indicates that your Worcester Bosch boiler has detected an ionisation current — in other words,… Read more →
- FA 364 The FA 364 code is a locking fault that appears when the boiler's internal self-diagnostic test detects that the EV2… Read more →
- FB The FB fault code (most commonly displayed as FB 365) means the boiler's internal safety system has run a leak test on… Read more →
- FB 365 The FB 365 code appears when your Worcester Bosch boiler's internal self-diagnostic routine has run a leak test on the… Read more →
- FD The FD code appears on your Worcester Bosch boiler's display to indicate that the unit has detected an interruption to… Read more →
- H07 H07 is a maintenance/blocking code — identified by its 'H' prefix — that appears on Worcester Bosch Greenstar boilers… Read more →
Greenstar 8000 series (Life & Style) codes
- 1010 The 1010 fault code (often displayed as '1010 O' on the boiler display) indicates that the boiler's EMS-Bus (Energy… Read more →
- 1017 The 1017 W fault code appears on Worcester Bosch boilers — most commonly the Greenstar 8000 series — when the system… Read more →
- 1021 Fault code 1021 indicates that the boiler's hot water (cylinder charging) temperature sensor — a small NTC thermistor —… Read more →
- 1022 Fault code 1022 appears on certain Worcester Bosch Greenstar boilers — particularly older CDi and conventional… Read more →
- 1037 Fault code 1037 is a blocking error on Worcester Bosch boilers that points to a problem with the flow temperature… Read more →
- 1065 Fault code 1065 on a Worcester Bosch boiler indicates that the boiler's control board cannot obtain a valid signal from… Read more →
- 1068 The 1068 W code appears on Worcester Bosch boilers when the external outdoor temperature sensor — an optional weather… Read more →
- 1073 Fault code 1073 W appears on Worcester Bosch Greenstar 8000 series boilers and indicates that the flow temperature… Read more →
- 1074 Fault code 1074 (often displayed as 1074 W) appears on Worcester Bosch Greenstar 8000 series boilers when the control… Read more →
- 1075 Fault code 1075 W on a Worcester Bosch boiler indicates that the heating circuit pump has been detected as blocked or… Read more →
- 1076 Fault code 1076 W appears on Worcester Bosch Greenstar 8000 series boilers when the control board stops receiving a… Read more →
- 2920 The 2920 is a cause code on Worcester Bosch boilers that points specifically to the heating circuit pump being blocked… Read more →
- 2924 Fault code 2924 is a locking error that causes the boiler to shut down completely and refuse to restart without a… Read more →
- 2925 Fault code 2925 appears on the Worcester Bosch Greenstar 2000 range and indicates that the boiler's internal… Read more →
- 2927 Fault code 2927 (sometimes displayed as 2927 B, where the 'B' denotes a blocking error rather than a full lockout)… Read more →
- 2946 Fault code 2946 (sometimes displayed as '2946 V') means the boiler's burner control unit has detected that the code… Read more →
- 2948 Fault code 2948 appears on Worcester Bosch Greenstar boilers when the burner control unit fires at high output but… Read more →
- 2950 Fault code 2950 means the boiler attempted to light the burner but the control board received no confirmation that a… Read more →
- 2963 Fault code 2963 is a cause code on Worcester Bosch boilers, meaning it appears alongside a primary blocking or locking… Read more →
- 2964 Fault code 2964 (sometimes displayed as 2964 B) appears on Worcester Bosch boilers when the control board detects that… Read more →
- 2965 Fault code 2965 appears on Worcester Bosch Greenstar 8000 series boilers and indicates that the water temperature… Read more →
- 2966 Fault code 2966 appears on Worcester Bosch Greenstar 8000 and Greenstar 2000 series boilers when the heat exchanger's… Read more →
- 2967 Fault code 2967 appears on Worcester Bosch Greenstar 8000 series boilers and signals that the control board has… Read more →
- 2970 Fault code 2970 appears on Worcester Bosch boilers when the system pressure is falling more rapidly than expected —… Read more →
- 2971 Fault code 2971 (sometimes shown as 2971 B on the display) appears exclusively on the Worcester Bosch Greenstar 8000… Read more →
Flashing-light patterns (older Greenstar CDi)
- 1 Long Flash The 1 Long Flash fault code is specific to Worcester Bosch Greenstar Ri boilers — models that use a flashing blue mains… Read more →
- 2 Long Flashes On older Worcester Bosch boilers fitted with a control box (such as the Danfoss-style unit), the diagnostic light… Read more →
- 3 Long Flashes The 3 long flashes fault code appears on older Worcester Bosch Greenstar models that use a flashing blue indicator… Read more →
- 4 Long Flashes On older Worcester Bosch boilers that use an LED flash sequence instead of an alphanumeric display, faults are… Read more →
- 4 Quick Flashes On Worcester Bosch boilers that use a flashing LED display rather than a digital readout, four rapid flashes followed… Read more →
- 5 Long Flashes On older Worcester Bosch models that use a flashing LED rather than a digital display — most notably the Greenstar 24i… Read more →
- Fast Flash A fast-flashing light on a Worcester Bosch boiler is the boiler's way of signalling a code plug problem — specifically… Read more →
- Slow Flash On most modern Worcester Bosch boilers, a slowly flashing blue light is not a fault condition at all — it simply means… Read more →