Worcester Bosch Boiler Error Codes

Worcester Bosch is renowned for producing reliable and efficient boilers, but even the best systems can encounter issues. Understanding the error codes associated with Worcester Bosch boilers can help diagnose and resolve problems quickly, ensuring your heating system remains in top shape.

This guide walks you through the most common error codes for various Worcester Bosch boiler models and their meanings.

Types of Worcester Bosch faults

Boilers are sophisticated appliances with numerous internal components that can potentially fail or malfunction. To help identify and address these issues, Worcester Bosch equips its boilers with a comprehensive set of error codes.

These codes are designed to clearly indicate various problems, although the specific codes and their meanings can vary slightly between different models.

Blocking error

A blocking error occurs when there's a blockage within the boiler's system, such as a clog in the condensate pipe. Unlike other errors, a blocking error doesn’t display a specific code. Instead, the boiler will shut down entirely.

To diagnose this, press the spanner/return button on your boiler. Once the blockage is cleared, the boiler should resume normal operation.

Locking error

If your boiler has a locking error, it will display a flashing fault code with a triangle and a static 'cause' code.

How do you reset the warning triangle on a Worcester boiler?

To reset the warning triangle on a Worcester boiler, first ensure that the underlying issue has been resolved. Then, turn off the boiler, wait a few minutes, and turn it back on.

If the reset is successful, the warning triangle should disappear. If the problem persists, consult the boiler’s manual or contact a professional for further assistance.

Maintenance code

Maintenance codes, identified by codes starting with ‘H’, do not halt boiler operation but indicate a need for professional attention. While these codes are not emergencies, they should be addressed to maintain the efficiency and safety of your system.

Cause error

A cause error is a three-digit code displayed on the interface during a blocking error. Press the return button to view this code. For locking errors, the cause error code will flash intermittently on the screen.

Fault error

Fault errors are indicated by an alphanumeric code, such as E119. These codes signal specific faults that need to be addressed to restore proper boiler function.

Worcester Bosch fault & error codes by boiler model

Worcester Bosch Greenstar i System/Combi error codes

The Worcester Bosch Greenstar i is a highly regarded boiler that has earned a reputation for reliability and efficiency. It is available in both system and combi models, making it a versatile choice for various household heating needs.

The Greenstar i comes in two main sizes: the 24i, suitable for smaller homes and apartments, and the 30i, designed for medium-sized homes with one bathroom. This model was recently replaced by the updated Greenstar 4000 series but remains popular for its excellent performance and ease of use.

Error code	Problem
A1	Pump stuck or running dry.
A7	Domestic hot water sensor defect.
A8	Heat control module (HCM) invalid.
C1	Fan stopping during operation.
C4	Control box or HCM defective.
C4	The fan has failed to stop.
C6	Fan speed is too high or too low.
C7	The fan is not running on start-up.
CC	Outdoor sensor defect.
D4	Primary flow temps rising too fast.
E2	Flow temperature issue.
E9	Flue or high limit thermostat activated.
E9	The primary flow temperature exceeds 95°C.
EA	No ionisation was detected after ignition.
FA	Ionisation is detected after the gas valve has closed.
F0	Gas valve/control box error.
F7	Ionisation was detected before the burner started.
FD	Power interrupted.
9U	Control box defective or loose.

Worcester Bosch Greenstar Si Compact error codes

The Worcester Bosch Greenstar Si Compact is designed to be a space-saving solution for smaller homes. This compact model offers a reliable and efficient heating solution without compromising on performance. It is known for its ease of installation and user-friendly interface, making it a popular choice for those seeking a high-performance boiler in a compact form.

Error code	Problem
9A 362	Incorrect Heat Control Module (HCM) fitted.
9U 233	HCM error or problem with the code plug.
A1 281	The pump is stuck or running with air in the system.
B7 257	Internal error or potential control board problem.
C1 264	Airflow stopped during operation.
C4 273	Airflow was present during the last 24 hours.
C6 215	Fan problem: Fan running too fast.
C7 214	Fan problem: Fan not running.
D1 240	Return sensor error: The sensor may be wet or damaged.
D1 240	Return sensor short circuit.
D4 271	The temperature difference between the flow and safety sensor exceeds its limit.
E2 222	Flow sensor short circuit error.
E5 218	The flow temperature is too high.
E9 219	Safety sensor fault: Temperature is too high, sensor short circuit or open circuit.
E9 224	Max thermostat activated or flue gas thermostat overheating.
EA 227	No flame detected or flame signal loss during operation.
EA 227	No ionisation was detected after ignition.
EF 349	Central heating boil detected: Boiler operating at minimum burner load with a temperature difference greater than 18°C between flow and return.
F0 237	Internal error.
F7 228	Flame error: False flame or flame detected before the burner started.
FA 306	False flame fault: Flame detected after the burner stopped.
FA 364	Gas valve EV2 leak test failed: Possible gas valve leak.
FB 365	Gas valve EV1 leak test failed: Possible gas valve leak.
FD 231	Mains power fault or electrical power interruption.
NO CODE 212	Safety or flow temperature rising too fast.
T1	Ignition test.
T2	Fan test.
T3	Pump test.
T4	Three-way valve test.
T6	Ionisation oscillator test.

Worcester Bosch CDi Classic Regular error codes

The Worcester Bosch CDi Classic Regular is known for its reliability and performance in providing consistent heating and hot water. This model is ideal for traditional heating systems and is designed to handle higher demands with ease. It’s well-suited for larger homes or properties with higher heating requirements.

Error code	Problem
B1	The code plug is not detected.
C6	Fan speed is too low or too high.
E2	Central heating (CH) flow negative temperature coefficient (NTC) sensor defective.
E9	The safety temperature limiter in the CH flow has tripped.
EA	Flame not detected.
F0	Internal error.
F7	Flame detected even though the appliance is switched off.
FA	Flame detected after the gas has been shut off.
FD	The reset button has been pressed by mistake.

Worcester Bosch CDi Compact error codes

The Worcester Bosch CDi Compact is a more compact version of the classic CDi model, designed to fit into smaller spaces while still providing robust heating and hot water capabilities. It’s a good choice for homes where space is at a premium but reliable performance is still required.

Error code	Problem
A1 281	The pump is stuck or running with air in the system.
B7 257	Internal error or a potential control board problem.
C1 264	Airflow stopped during operation.
C4 273	Airflow was present during the last 24 hours.
C6 215	Fan problem: Fan running too fast.
C7 214	Fan problem: Fan not running.
D1 240	Return sensor error: The sensor may be wet or damaged.
D1 240	Return sensor short circuit.
D4 271	The temperature difference between the flow and safety sensor exceeds its limit.
E2 222	Flow sensor short circuit error.
E5 218	The flow temperature is too high.
E9 219	Safety sensor fault: The temperature is too high, sensor short circuit or open circuit.
E9 224	Max thermostat activated or flue gas thermostat overheated.
EA 227	No flame detected or flame signal loss during operation.
EF 349	Central heating boil detected: Boiler operating at a minimum burner load with a temperature difference greater than 18°C between flow and return.
F0 237	Internal error.
F7 228	Flame error: False flame or flame detected before the burner started.
FA 306	False flame fault: Flame detected after burner stopped.
FA 364	Gas valve EV2 leak test failed: Possible gas valve leak.
FB 365	Gas valve EV1 leak test failed: Possible gas valve leak.
FD 231	Mains power fault or electrical power interruption.
NO CODE 212	Safety or flow temperature is rising too fast.
T1	Ignition test.
T2	Fan test.
T3	Pump test.
T4	Three-way valve test.
T6	Ionisation oscillator test.
9A 362	Incorrect HCM fitted.
9U 233	HCM error or problem with the code plug.

Worcester Bosch CDi Classic Combi error codes

The Worcester Bosch CDi Classic Combi is a reliable choice for homes requiring both heating and hot water on demand. Its compact design and high performance make it suitable for various home sizes, offering efficient and dependable service.

Error code	Problem
A1	Water is leaking, or the pump needs replacing or freeing due to the pump running dry.
A7	The hot water negative temperature coefficient (NTC) sensor is defective. The hot water sensor or connecting leads need checking.
A8	Break communication to FX sensor controls: Electrical connections need checking.
B1	Code plug not detected.
C6	The fan speed is too low. The fan lead and connector need checking and may need replacing.
E2	Central heating (CH) water flow negative temperature coefficient (NTC) sensor defective: Check the CH flow, NTC sensor and connection leads.
E9	The safety temperature limiter in the central heating (CH) flow has tripped the system pressure, or the safety temperature limiter needs checking.
EA	No flame was detected due to a gas issue. The gas supply, power supply or igniter, electrode, and lead need checking.
FO	An issue with the electrical connector contacts or programmer interface module. Check the ignition leads are not loose.
F7	Flame detected even though the appliance is switched off. Check the electrode assembly is dry and that the PCB and flue are clear.
FA	Flame detected after the gas has been shut off. The gas valve needs checking.
FD	The reset button was pressed by mistake. Press the reset button again.

Worcester Bosch CDi Highflow error codes

The Worcester Bosch CDi Highflow is designed for larger homes or properties with high heating demands. Its robust build and high capacity make it a suitable choice for extensive heating systems, providing reliable performance for greater needs.

Error code	Problem
A1	Pump dry run detection or the pump is letting air into the system: The pressure needs checking.
A5	Tank negative temperature coefficient (NTC) defect.
A7	Domestic hot water (DHW) negative temperature coefficient (NTC) defect.
A8	Energy Management System (EMS) communication error.
B1	Code plug not detected.
B2, B3, B4, B5, B6	Data error.
B7	Burner control error.
C6	Fan defect.
D3	External temperature limiter.
D5	Condensate pump failure.
D6	Internal heat bank overflow.
EA	Flame not detected.
E2	Primary negative temperature coefficient (NTC) defect.
E9	The safety temperature limiter in the central heating (CH) flow stat has tripped.
F0	Internal error.
F1	ROM fault.
F7	Flame detected after the appliance has been shut off.
FA	Flame detected after the gas has been shut off.
FD	The reset button was pressed accidentally. Try pressing the reset button again.

Worcester Bosch 8000 Style error codes

The Worcester Bosch 8000 Style series represents the latest in boiler technology, combining advanced features with sleek design. These boilers offer high efficiency and ease of use, making them a popular choice for modern homes seeking a blend of style and performance.

Error code	Problem
200 O	Boiler in heating mode.
201 O	The fan is not running on start-up.
202 O	Boiler in anti-cycle mode.
203 O	Boiler in standby mode.
204 O	The current primary water temperature is higher than the set value.
208 O	Chimney sweep demand.
224 V	The safety temperature limiter has tripped. Top up the water until the preset pressure is reached.
227 V	No flame signal after ignition. The burner control unit could need replacing.
228 V	Flame signal without a flame present. The air/gas ratio control valve may need replacing, as might the ionisation cable.
305 O	Boiler in hot water anti-cycle mode.
306 V	Flame signal after closing the fuel supply. The air/gas ratio control valve might need to be replaced.
360 V	Incompatible code plug. Check if a correct code plug is installed and replace or reconnect the code plug.
815 W/B	Low loss header temperature sensor faulty. Check the sensor port or check the differential sensor for incorrect installation position or breakage.
1010 O	No BUS communication cable, EMS-Bus isn’t connected or damaged. Connect the cable for the EMS-Bus or replace the damaged cable exchange fuse.
1017 W	The water pressure is too low. The water needs topping up, and the vent system or pressure sensor may need replacing.
1021 B	The hot water temperature sensor is defective. The plug to the hot water temperature sensor may not be connected.
1022 B	The hot water storage temperature sensor is defective. Connect the plug to the hot water temperature sensor correctly, mount the hot water temperature sensor correctly, or replace the hot water temperature sensor.
1037 W	The outside temperature sensor is defective. Check the connecting lead.
1065 B	The pressure sensor is faulty or not connected. Check the pressure sensor connection, as it may need to be replaced.
1068 W	The outside temperature sensor is defective. Check the connecting lead.
1073 W	Short circuit of the flow temperature sensor. The temperature sensor may need to be replaced.
1074 W	No signal from the flow temperature sensor. Connect the plug to the flow temperature sensor correctly, or the temperature sensor could need to be replaced.
1075 W	Short circuit of the temperature sensor at the heating block. The temperature sensor may need replacing.
1076 W	No signal from the temperature sensor at the heating block. Replace the temperature sensor, the connecting lead or the control unit.
2920 V	Error with the flame monitoring.
2924 V	No feedback from the modulating gas valve or the gas valve relay is defective. Press the reset button and apply the burner start. Wait to see if the fault reoccurs; if it does, the gas valve likely needs to be replaced.
2925 V	Feedback from the modulating gas valve is too low.
2927 B
2927 B	The flame failed during the burner operation. To resolve, try: ● Opening the main shut-off valve, shutting down the appliance and checking the gas line ● Replacing the ionisation electrode ● Setting the burner and minimum rated load correctly ● Checking the integrity of the flue system and if the interconnected room air supply is too small ● Cleaning the heating block on the flue gas side ● Replacing the control unit/burner control unit
2946 V	Incorrect code plug detected. The code plug needs to be replaced.
2948 B	No flame signal. With low output, the burner starts automatically after cleaning. If the fault occurs repeatedly, the setting of the CO2 valves needs checking.
2963 B	The signal from the flow and heat exchanger temperature sensor is outside the permissible range. The connecting lead needs to be connected correctly.
2964 B	The flow rate in the heat exchanger is too low.
2965 B	The flow temperature is too high.
2966 B	The flow temperature heat exchanger is rising too fast.
2967 B	The flow/heat exchanger temperature sensor differential is too great.
2970 B	The pressure drop in the heating system is too fast.
2971 B	The system pressure is too low. The heating system needs venting, or water needs topping up until the preset pressure is reached. Replace the cable to the pressure sensor or replace the pressure sensor.

When to call in a JustFix professional

If you encounter persistent error codes or issues with your Worcester Bosch boiler that you can’t resolve on your own, it’s wise to consult a professional.

JustFix connects you with qualified heating and gas engineers who can diagnose and repair problems with fixed, transparent pricing.

Our experts are equipped to handle all types of boiler faults and ensure your heating system runs smoothly. Whether you’re dealing with a blocking error or a complex fault code, JustFix provides reliable and affordable solutions to keep your home comfortable.