Worcester Bosch fault & error codes

Upon realising your Worcester Bosch boiler has stopped working, you will likely see an error code displayed on the system's interface. These codes enable engineers to determine the problem with the boiler, especially if the issue isn't evident from other telltale signs right away.

There are a lot of potential issues that can arise with your boiler. To make the process easier, in this blog, we'll cover all of the most common error codes so that you can ensure any problems are resolved as quickly as possible.

In the majority of cases, it’s best to contact a Gas Safe registered engineer to carry out a boiler service if you are experiencing issues with your boiler. They will have the training and qualifications needed to carry out any investigations or repairs needed safely.

Worcester Bosch fault & error codes by boiler model

• Worcester Bosch Greenstar i System/Combi Boiler error codes
• Worcester Bosch Greenstar Si Compact error codes
• Worcester Bosch CDi Classic Regular boiler
• Worcester Bosch CDi Compact error codes
• Worcester Bosch CDi Classic Combi Boiler error codes
• Worcester Bosch CDi Highflow error codes
• Worcester Bosch 8000 Style error codes

Worcester Bosch boiler error codes

Boilers are incredibly complex pieces of kit with huge numbers of internal components, all of which can stop working as they should. 

To effectively diagnose each possible problem, Worcester Bosch pre-programs its boilers with long lists of error codes, which often differ slightly depending on the exact model in question.

Blocking error

If your boiler has a blockage somewhere in its system (such as in its condensate pipe), it will experience what’s known as a blocking error. Unlike other types of faults, no error code will be displayed on the screen; the boiler will simply power down and stop working altogether. 

You'll need to press the spanner/return button to diagnose the cause of the blockage, and the boiler will begin working again once it’s been cleared.

Locking error

If your boiler has a locking error, it will display a flashing fault code with a triangle. It will also display a static "cause" code. Once the issue has been repaired, the boiler will need resetting in order to erase the code.

Maintenance code

Maintenance codes can be identified as any code that is displayed that begins with an ‘H’. This fault won't stop the boiler from operating altogether but will still need to be looked at by an engineer.

Cause error

A cause error is a three-digit number that is found on your interface when looking for the block code. It can be seen by pressing the return button when a blocking error is happening. Note that when your boiler is experiencing a locking error, the cause error code should flash intermittently on the screen.

Fault error

If your boiler is experiencing a fault, an initial fault code will show. This will be an alphanumeric code, such as E119.

Worcester Bosch Greenstar i System/Combi error codes

The Worcester Bosch Greenstar i has been installed in over a million UK homes, making it one of the brand's best-selling combi boiler models. This model is also available as a system boiler, and both types use the same error codes shown below.

The Greenstar i is an award-winning boiler that comes in two sizes: the 24i, which has a 24-kilowatt capacity and is perfect for small apartments and homes, and the 30i, which has a 30-kilowatt capacity and is more appropriate for a typical 3-bedroom house with one bathroom.

This model was recently discontinued and replaced by the new and improved Greenstar 4000.

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 has very similar credentials to the Greenstar i mentioned earlier. It’s an energy-efficient boiler option, making it popular for small and medium-sized properties.

The clue is in the name. The key difference here is the Greenstar Si Compact is designed to fit into smaller spaces within a home, such as airing cupboards or kitchen cabinets. This makes it perfect for anyone looking to box their boiler in to keep it out of sight or those who have limited available storage space.

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 was one of the brand’s most popular boilers until it was replaced by the newer, more efficient Greenstar 8000 Style. 

The CDi Classic range included both combi and standard models and offered different power ratings, including 29kW, 34kW, 38kW, and 42kW. This wide range of options meant it was suitable for small, medium and large homes with varying heating and hot water 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

Another popular combi boiler from Worcester Bosch is the CDi Compact. This has power outputs of 28 kW, 32 kW, and 34 kW, making it perfect for small and medium-sized properties.

As its name suggests, this boiler is compact, so it’s ideal for ‘boxed-in’ installations within kitchen cabinets or custom-built units. If you’re searching for a combi boiler that’s easy to conceal without making any compromises on performance, you’ll struggle to go wrong with the CDi Compact.

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 combination boiler was launched in 2012 and was the brand's flagship model before being replaced by the Worcester Bosch 8000.

In its heyday, the CDi Classic was Worcester Bosch’s most powerful combination boiler, offering a range of power ratings to meet varying hot water demands. The 29kW and 34kW models were popular for smaller homes, and the 38kW and 42kW were designed specifically for larger properties.

Error code	Problem / Solution
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

Known for its industry-leading hot water flow rates, the Worcester Bosch CDi Highflow is a robust floor-standing combi boiler and one of the best Worcester Bosch has to offer.

Large homes with numerous bathrooms that don't want to make room for an additional water tank are perfect candidates for this model. When it comes to output, few boilers can compare to it.

Error	Problem / Solution
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 is one of the manufacturer’s latest models in its impressive Greenstar range.

It's the brand's most powerful boiler model, available in power outputs from 30kW all the way up to 45kW. This boiler is a perfect option for large homes or households with particularly high hot water demands.

The boiler's exterior is a talking point of this model, as it offers homeowners a unique and impressive aesthetic with its wall-hung design. Although it's a stylish-looking boiler, style isn't a substitute for power in this model. This model is available in black and white finishes.

Error code	Problem / Solution
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	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.

Protect your home’s central heating with BOXT

Luckily, the majority of Worcester Bosch boiler problems are relatively quick and easy for qualified engineers to fix, provided they’re identified promptly. If you suspect that any of the issues mentioned above are to blame for your boiler’s malfunctioning, and the recommended fix isn’t as simple as pressing the reset button, always contact a Gas Safe registered engineer who’ll be able to come and assist you.