Worcester Bosch
Worcester Bosch Water Heaters Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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A1
Boiler shows A1 and stops, often accompanied by gurgling sounds, condensate may not be draining.
Condensate Drain Blocked
A7
Boiler displays A7, hot water temperature may be incorrect or boiler may not respond to demand correctly.
Flow Temperature Sensor / Control Sensor Fault
A8
Boiler shows A8, may not respond correctly to room thermostat or controls.
Control Interface / Bus Communication Fault
A9
Boiler displays A9, may have issues with hot water temperature regulation.
DHW Outlet Temperature Sensor Fault
C6
Boiler shows C6, fan may run at incorrect speed or not be detected correctly.
Fan Speed / Tacho Fault
C7
Boiler displays C7, fan does not start or is not recognised.
Fan Not Running / Fan Supply Fault
D1
Boiler shows D1, may indicate a problem with the pump or flow through the boiler.
Pump / Flow Fault
D5
Boiler displays D5, may not respond correctly to external controls or sensors.
Sensor / Control Input Fault
E1 218
Boiler shows E1 218 and will not fire, fan may not run or runs briefly then stops.
Fan Speed / Airflow Fault
E1 227
Boiler displays E1 227, attempts to ignite but fails, often after running out of gas or after gas supply interruption.
No Flame Signal / Flame Loss During Ignition
E1 234
Boiler shows E1 234, may indicate flue gas recirculation or combustion issues.
Flue Gas Recirculation / Combustion Fault
E1 256
Boiler displays E1 256, may not start or may shut down unexpectedly.
Internal Communication / PCB Fault
E1 332
Boiler displays E1 332, may run briefly then shut down, often associated with incorrect combustion.
Flame Signal / Combustion Quality Fault
E1 338
Boiler shows E1 338, may indicate unstable flame or ionisation signal.
Unstable Flame / Ionisation Fault
E2
Boiler shows E2 and shuts down, may occur intermittently, often related to temperature sensing.
Flow Temperature Sensor (NTC) Fault
E3
Boiler displays E3, may run briefly then stop, often associated with return temperature sensing.
Return Temperature Sensor (NTC) Fault
E5
Boiler shows E5, may not start or may shut down during operation, often related to fan or air pressure.
Air Pressure / Fan Proving Fault
E6
Boiler displays E6, hot water temperature unstable or boiler shuts down when hot water is drawn.
Hot Water Temperature Sensor (DHW NTC) Fault
E9
Boiler shows E9 and shuts down, may attempt to start then quickly lock out, flow temperature may rise rapidly.
Overheat / Safety Temperature Limiter Trip
E9 224
Boiler locks out with E9 224, often after overheating, may require manual reset.
Safety Temperature Limiter (STL) Lockout
EA
Boiler locks out with EA on display, burner does not ignite, you may hear clicking from the ignition but no flame established.
Ignition Failure / Flame Not Detected
H07
Boiler displays H07, may indicate a problem with the diverter valve or hot water priority.
Diverter Valve Positioning Fault
H11
Boiler shows H11, may not respond to hot water demand or may give priority issues.
Flow Switch / DHW Demand Detection Fault
U9
Boiler displays U9, may indicate an issue with the user interface or parameter settings.
User Interface / Parameter Fault
Symptom
Boiler display is on but completely blank or unreadable, controls unresponsive.
User Interface Failure
Symptom
Boiler fan runs but burner does not light, no error code displayed initially.
Ignition Sequence Incomplete
Symptom
Boiler flue dripping water externally or staining the wall.
Condensate Leakage from Flue
Symptom
Boiler frequently needs resetting, with no consistent error code, especially during hot water use.
Intermittent Overheat / Flow Restriction
Symptom
Boiler frequently short cycles (turns on and off rapidly) when heating.
Oversized Boiler / Poor System Design or Sensor Placement
Symptom
Boiler locks out occasionally when it is very windy outside.
Flue Terminal Affected by Wind / Pressure Fluctuations
Symptom
Boiler losing pressure regularly, pressure gauge drops to zero and boiler locks out.
System Water Leak / Expansion Vessel Failure
Symptom
Boiler makes loud banging or kettling noises when heating water.
Primary Heat Exchanger Scaled or Sludged
Symptom
Boiler runs but produces lukewarm hot water only, even at low flow rates.
Insufficient DHW Output / Modulation Fault
Symptom
Boiler runs but radiators do not get hot, hot water is available on a combi or system boiler.
Heating Circuit Flow Problem
Symptom
Boiler will not start at all, no display or lights on Worcester Bosch appliance.
No Power / Electrical Supply Fault
Symptom
Intermittent hot water temperature: water runs hot then cold on a Worcester Bosch combi.
Plate Heat Exchanger Partially Blocked
Symptom
No hot water but central heating works normally on a Worcester Bosch combi boiler.
Diverter Valve Stuck in Heating Position
Symptom
Radiators get hot when only hot water is demanded on a combi boiler.
Diverter Valve Passing to Heating Circuit
Symptom
Strong smell of gas near the Worcester Bosch boiler.
Gas Leak
Symptom
Water leaking from the bottom of the Worcester Bosch boiler casing.
Internal Water Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| A1 |
Boiler shows A1 and stops, often accompanied by gurgling sounds, condensate may not be draining.
|
Condensate Drain Blocked | View Details |
| A7 |
Boiler displays A7, hot water temperature may be incorrect or boiler may not respond to demand correctly.
|
Flow Temperature Sensor / Control Sensor Fault | View Details |
| A8 |
Boiler shows A8, may not respond correctly to room thermostat or controls.
|
Control Interface / Bus Communication Fault | View Details |
| A9 |
Boiler displays A9, may have issues with hot water temperature regulation.
|
DHW Outlet Temperature Sensor Fault | View Details |
| C6 |
Boiler shows C6, fan may run at incorrect speed or not be detected correctly.
|
Fan Speed / Tacho Fault | View Details |
| C7 |
Boiler displays C7, fan does not start or is not recognised.
|
Fan Not Running / Fan Supply Fault | View Details |
| D1 |
Boiler shows D1, may indicate a problem with the pump or flow through the boiler.
|
Pump / Flow Fault | View Details |
| D5 |
Boiler displays D5, may not respond correctly to external controls or sensors.
|
Sensor / Control Input Fault | View Details |
| E1 218 |
Boiler shows E1 218 and will not fire, fan may not run or runs briefly then stops.
|
Fan Speed / Airflow Fault | View Details |
| E1 227 |
Boiler displays E1 227, attempts to ignite but fails, often after running out of gas or after gas supply interruption.
|
No Flame Signal / Flame Loss During Ignition | View Details |
| E1 234 |
Boiler shows E1 234, may indicate flue gas recirculation or combustion issues.
|
Flue Gas Recirculation / Combustion Fault | View Details |
| E1 256 |
Boiler displays E1 256, may not start or may shut down unexpectedly.
|
Internal Communication / PCB Fault | View Details |
| E1 332 |
Boiler displays E1 332, may run briefly then shut down, often associated with incorrect combustion.
|
Flame Signal / Combustion Quality Fault | View Details |
| E1 338 |
Boiler shows E1 338, may indicate unstable flame or ionisation signal.
|
Unstable Flame / Ionisation Fault | View Details |
| E2 |
Boiler shows E2 and shuts down, may occur intermittently, often related to temperature sensing.
|
Flow Temperature Sensor (NTC) Fault | View Details |
| E3 |
Boiler displays E3, may run briefly then stop, often associated with return temperature sensing.
|
Return Temperature Sensor (NTC) Fault | View Details |
| E5 |
Boiler shows E5, may not start or may shut down during operation, often related to fan or air pressure.
|
Air Pressure / Fan Proving Fault | View Details |
| E6 |
Boiler displays E6, hot water temperature unstable or boiler shuts down when hot water is drawn.
|
Hot Water Temperature Sensor (DHW NTC) Fault | View Details |
| E9 |
Boiler shows E9 and shuts down, may attempt to start then quickly lock out, flow temperature may rise rapidly.
|
Overheat / Safety Temperature Limiter Trip | View Details |
| E9 224 |
Boiler locks out with E9 224, often after overheating, may require manual reset.
|
Safety Temperature Limiter (STL) Lockout | View Details |
| EA |
Boiler locks out with EA on display, burner does not ignite, you may hear clicking from the ignition but no flame established.
|
Ignition Failure / Flame Not Detected | View Details |
| H07 |
Boiler displays H07, may indicate a problem with the diverter valve or hot water priority.
|
Diverter Valve Positioning Fault | View Details |
| H11 |
Boiler shows H11, may not respond to hot water demand or may give priority issues.
|
Flow Switch / DHW Demand Detection Fault | View Details |
| U9 |
Boiler displays U9, may indicate an issue with the user interface or parameter settings.
|
User Interface / Parameter Fault | View Details |
| – |
Boiler display is on but completely blank or unreadable, controls unresponsive.
|
User Interface Failure | View Details |
| – |
Boiler fan runs but burner does not light, no error code displayed initially.
|
Ignition Sequence Incomplete | View Details |
| – |
Boiler flue dripping water externally or staining the wall.
|
Condensate Leakage from Flue | View Details |
| – |
Boiler frequently needs resetting, with no consistent error code, especially during hot water use.
|
Intermittent Overheat / Flow Restriction | View Details |
| – |
Boiler frequently short cycles (turns on and off rapidly) when heating.
|
Oversized Boiler / Poor System Design or Sensor Placement | View Details |
| – |
Boiler locks out occasionally when it is very windy outside.
|
Flue Terminal Affected by Wind / Pressure Fluctuations | View Details |
| – |
Boiler losing pressure regularly, pressure gauge drops to zero and boiler locks out.
|
System Water Leak / Expansion Vessel Failure | View Details |
| – |
Boiler makes loud banging or kettling noises when heating water.
|
Primary Heat Exchanger Scaled or Sludged | View Details |
| – |
Boiler runs but produces lukewarm hot water only, even at low flow rates.
|
Insufficient DHW Output / Modulation Fault | View Details |
| – |
Boiler runs but radiators do not get hot, hot water is available on a combi or system boiler.
|
Heating Circuit Flow Problem | View Details |
| – |
Boiler will not start at all, no display or lights on Worcester Bosch appliance.
|
No Power / Electrical Supply Fault | View Details |
| – |
Intermittent hot water temperature: water runs hot then cold on a Worcester Bosch combi.
|
Plate Heat Exchanger Partially Blocked | View Details |
| – |
No hot water but central heating works normally on a Worcester Bosch combi boiler.
|
Diverter Valve Stuck in Heating Position | View Details |
| – |
Radiators get hot when only hot water is demanded on a combi boiler.
|
Diverter Valve Passing to Heating Circuit | View Details |
| – |
Strong smell of gas near the Worcester Bosch boiler.
|
Gas Leak | View Details |
| – |
Water leaking from the bottom of the Worcester Bosch boiler casing.
|
Internal Water Leak | View Details |
No matching codes found
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