Worcester Bosch is one of the UK’s most trusted boiler brands, established in 1962. Their Greenstar range is installed in over 1 in 3 UK homes. Worcester Bosch error codes vary by model — newer models use alphanumeric codes (EA, CE, C6, A1) while older CDi models may use numeric codes with letter suffixes.
Worcester Bosch Boiler Fault Codes
All Worcester Bosch Fault Codes 80
| Code | Fault | Severity | Type | View guide |
|---|---|---|---|---|
| 1017 W | Low Water Pressure Warning (8000 Series) On Worcester Greenstar 8000 boilers, code 1017 W indicates the system water pressure is too… | Low | DIY Check | View Guide |
| 1065 B | Pressure Sensor Defective (8000 Series) On 8000 Series boilers, code 1065 B indicates the pressure sensor is not connected or… | Medium | Engineer | View Guide |
| 1073 W | Flow Temperature Sensor Short Circuit (8000 Series) On 8000 Series boilers, code 1073 W indicates a short circuit in the flow temperature… | Medium | Engineer | View Guide |
| 1074 W | Flow Temperature Sensor No Signal (8000 Series) On 8000 Series boilers, code 1074 W means the flow temperature sensor is not providing… | Medium | Engineer | View Guide |
| 224 V | Safety Temperature Limiter Tripped (8000 Series) On 8000 Series boilers, code 224 V means the safety temperature limiter has operated. 'V'… | High | Engineer | View Guide |
| 227 | Ignition Lockout (Older CDi Models) On older Worcester Greenstar CDi models, fault code 227 indicates ignition failure after multiple attempts. | Medium | DIY Check | View Guide |
| 227 V | No Flame Signal (8000 Series Lockout) On 8000 Series boilers, code 227 V is a lockout (V = lockout) for no… | Medium | DIY Check | View Guide |
| 2927 B | Flame Lost During Operation (8000 Series) On 8000 Series boilers, code 2927 B means the ionisation current was insufficient during the… | Medium | DIY Check | View Guide |
| 2948 B | No Flame Signal (8000 Series) On Greenstar 8000 boilers, code 2948 B indicates no flame signal was detected. At low… | Medium | Engineer | View Guide |
| 2948 V | Flue Gas Sensor Open Circuit The flue gas NTC circuit is broken. | Medium | Engineer | View Guide |
| 2965 B | Flow Temperature Too High (8000 Series) On 8000 Series boilers, code 2965 B means the flow temperature has exceeded safe limits. | High | Engineer | View Guide |
| 2965 V | Flue Gas Sensor Short Circuit The flue gas NTC has a short circuit. | Medium | Engineer | View Guide |
| 2970 B | System Pressure Drop Too Rapid (8000 Series) On 8000 Series boilers, code 2970 B means system pressure is dropping at an unusually… | High | Engineer | View Guide |
| 2971 B | System Pressure Too Low (8000 Series) On 8000 Series boilers, code 2971 B indicates system pressure is below the minimum. The… | Low | DIY Check | View Guide |
| 360 V | Incompatible Code Plug (8000 Series) On 8000 Series boilers, code 360 V means the code plug (boiler identification module) is… | Medium | Engineer | View Guide |
| 6A | Safety Fuse Fault The internal safety fuse has blown. This can be caused by tampering, poor maintenance, or… | High | Engineer | View Guide |
| 9U | Blocked Condensate / Condense Sensor The condensate system is blocked or the condensate sensor is indicating a problem. Most commonly… | Medium | DIY Check | View Guide |
| 9U 257 | Appliance Variant Not Set The boiler variant has not been correctly configured. | High | Engineer | View Guide |
| A1 | Pump Stuck or Running Dry The circulation pump is not running correctly — either it is seized, running without water,… | High | Engineer | View Guide |
| A21 | Thermostat / Receiver Communication Fault The boiler cannot communicate with the wireless thermostat receiver. Usually caused by low batteries in… | Low | DIY Check | View Guide |
| A21 281 | Pump Blockage / Circulation Fault The pump is blocked, preventing proper water circulation through the system. | High | Engineer | View Guide |
| A22 | Loss of RF Signal The boiler has lost the wireless radio frequency signal from the room thermostat. The thermostat… | Low | DIY Check | View Guide |
| A281 | Internal Water Leak Detected The boiler has detected an internal water leak. Water may be dripping onto internal components… | High | Engineer | View Guide |
| A61 | Gas Valve Fault There is a fault with the gas valve — it may not be opening or… | High | Engineer | View Guide |
| A7 | Flow Temperature Sensor Fault The flow NTC thermistor is giving a reading outside its expected range. Similar to E2,… | Medium | Engineer | View Guide |
| A7 246 | Diverter Valve Fault The diverter valve is not switching correctly between heating and hot water. | Medium | Engineer | View Guide |
| A8 | Return Temperature Sensor Fault The return NTC thermistor is giving an out-of-range reading. | Medium | Engineer | View Guide |
| A8 246 | DHW Thermistor Fault The domestic hot water NTC sensor has a fault. | Medium | Engineer | View Guide |
| B1 | PCB Internal Fault The main Printed Circuit Board has detected an internal error it cannot recover from. | High | Engineer | View Guide |
| B1 257 | Coding Plug Missing The boiler's coding plug is not detected. | High | Engineer | View Guide |
| B7 | Gas Valve Short Circuit A short circuit has been detected in the gas valve wiring or the valve itself. | High | Engineer | View Guide |
| B7 257 | Internal Communication Error There is an internal communication error between boiler components, typically involving the printed circuit board… | High | Engineer | View Guide |
| C1 | Fan Fault / Air Pressure Switch Fault The fan is not running at the correct speed or the air pressure switch is… | High | Engineer | View Guide |
| C1 221 | Flow Sensor Short Circuit The flow NTC sensor wiring has a short circuit. | Medium | Engineer | View Guide |
| C1 238 | Return Sensor Short Circuit The return NTC sensor wiring has a short circuit. | Medium | Engineer | View Guide |
| C4 | Flue Temperature Sensor Fault The flue gas temperature sensor is giving an out-of-range or implausible reading. | Medium | Engineer | View Guide |
| C4 218 | Air Pressure Switch Stuck Closed The APS is stuck in the closed position. | High | Engineer | View Guide |
| C6 | Fan Speed Error The boiler fan is not running at the correct speed. This prevents safe ignition as… | High | Engineer | View Guide |
| C7 | Fan Overspeed Error The boiler fan is running faster than its rated speed, which can indicate a fault… | High | Engineer | View Guide |
| CE 201 | Flow Temperature Sensor Fault The flow temperature sensor (NTC thermistor) has a fault in its wiring or the sensor… | Medium | Engineer | View Guide |
| CE 203 | Flow Sensor Fault The flow temperature sensor is giving an implausible or out-of-range reading. | Medium | Engineer | View Guide |
| CE 207 | Low Water Pressure The boiler's water pressure has dropped below the safe minimum level. One of the easiest… | Low | DIY Check | View Guide |
| CE 210 | Primary Flow Sensor Fault The primary flow NTC sensor is giving an out-of-range reading on modern Greenstar models. | Medium | Engineer | View Guide |
| D1 200 | Heating System Circulation Fault The boiler is detecting poor water circulation in the heating system. The temperature difference between… | Medium | Engineer | View Guide |
| D1 204 | Boiler Identification Module Fault The boiler's identification module (SCB) is not communicating correctly with the main PCB. Usually occurs… | Medium | Engineer | View Guide |
| D1 218 | Flow/Return Temp Difference Too High Poor circulation — the temperature gap between flow and return is abnormally large. | Medium | Engineer | View Guide |
| D3 | External Thermostat Short Circuit The external thermostat or room controller wiring has a short circuit. The boiler cannot receive… | Medium | Engineer | View Guide |
| D3 218 | External Thermostat Circuit Fault The wiring from the room thermostat has a fault. | Medium | Engineer | View Guide |
| D4 | System Purge Required / Air in System Air has been detected in the primary circuit after a period of non-use or maintenance… | Low | DIY Check | View Guide |
| D5 | Primary Flow Thermistor Fault The main flow temperature sensor is giving an out-of-range reading, preventing the boiler from monitoring… | Medium | Engineer | View Guide |
| E2 | Flow NTC Sensor Fault The flow temperature sensor (NTC thermistor) is giving an incorrect reading — either out of… | Medium | Engineer | View Guide |
| E2 218 | Flow Temperature Sensor Fault The flow temperature NTC sensor has developed a fault. It may be reading incorrectly or… | Medium | Engineer | View Guide |
| E5 | Flow Temperature Too High The boiler flow temperature has exceeded 105°C — the maximum safe limit. A serious overheat… | High | Engineer | View Guide |
| E5 218 | Flow Sensor Open Circuit The flow NTC circuit is broken. | Medium | Engineer | View Guide |
| E5 238 | Return Sensor Open Circuit The return NTC circuit is broken. | Medium | Engineer | View Guide |
| E9 | Overheat Fault The boiler's safety thermostat has detected dangerously high temperatures and triggered a lockout. Usually caused… | High | Engineer | View Guide |
| E9 219 | Safety Sensor Fault — Temperature Exceeded The safety temperature sensor has detected a temperature in excess of 105°C, or the sensor… | High | Engineer | View Guide |
| E9 224 | Overheat — Safety Limiter Tripped (Code 224) The safety temperature limiter has tripped due to overheating. Sub-code 224 typically indicates this occurred… | High | Engineer | View Guide |
| E9 277 | Safety Sensor High Temperature (GB162) On Worcester GB162 commercial boilers, code E9 277 means the safety temperature sensor has measured… | High | Engineer | View Guide |
| EA 227 | Ignition Failure / No Flame Detected The boiler has failed to detect a flame after four ignition attempts, triggering a safety… | Medium | DIY Check | View Guide |
| EA 229 | Flame Loss During Operation The boiler ignited successfully but then lost the flame during operation. Very common in winter… | Medium | DIY Check | View Guide |
| EA 234 | Flame Not Detected After Start The boiler attempted to start but could not detect a flame. Similar to EA 227,… | Medium | DIY Check | View Guide |
| EA 261 | Heat Control Module (HCM) Potentially Defective On Greenstar i boilers, EA 261 indicates the Heat Control Module (HCM) may be defective.… | Medium | DIY Check | View Guide |
| EA 306 | Flame Lost After 10 Seconds Flame established but lost within 10 seconds. | High | Engineer | View Guide |
| EA 338 | Flame Detected When Not Expected The boiler has detected a flame signal when the gas valve should be closed. This… | High | Engineer | View Guide |
| EF | Maximum Reset Count Exceeded The boiler has been reset too many times without the underlying fault being resolved, and… | High | Engineer | View Guide |
| EF 349 | Central Heating Boil Detected The boiler is operating at minimum burner load but the temperature difference between flow and… | High | Engineer | View Guide |
| F0 | Internal Component Fault A general internal fault code indicating a component has failed. The specific sub-code (e.g. F0… | High | Engineer | View Guide |
| F7 | Flame Detected After Shutdown (Unsafe) The boiler's ionisation circuit is detecting a flame signal when the gas valve should be… | High | Engineer | View Guide |
| FA | Flue Condensate Blocked / Siphon Full The condensate siphon inside the boiler is full or blocked, preventing the boiler from starting.… | Medium | DIY Check | View Guide |
| FA 306 | False Flame — Ionisation After Burner Stop The boiler has detected ionisation current (flame signal) after the burner has been commanded to… | High | Engineer | View Guide |
| FD | Temperature/Pressure Sensor Combination Fault Multiple sensor faults have been detected simultaneously, or the temperature/pressure combination is outside safe operating… | High | Engineer | View Guide |
| FD 231 | Mains Power Interrupted During Lockout The mains power supply was interrupted while the boiler was in a lockout state. This… | Low | DIY Check | View Guide |
| H02 | Central Heating Sensor Fault The central heating temperature sensor is giving an incorrect reading. | Medium | Engineer | View Guide |
| H02 218 | Status: Heating Demand The boiler is running to satisfy a central heating demand. Normal operation. | Medium | DIY Check | View Guide |
| H06 | Gas Valve Fault The gas valve is not operating correctly according to the boiler control system. | High | Engineer | View Guide |
| H06 218 | Status: DHW Demand The boiler is running to provide hot water. Normal operation. | Medium | DIY Check | View Guide |
| H07 | Low Water Pressure Warning A low pressure warning code displayed on some Worcester Greenstar models. The boiler may continue… | Low | DIY Check | View Guide |
| H07 218 | Status: Standby The boiler is in standby with no active demand. | Medium | DIY Check | View Guide |
| HRE | Boiler Resetting Frequently The boiler has been resetting itself repeatedly. This indicates a recurring fault that the boiler… | Medium | Engineer | View Guide |