Worcester Boiler Error Codes [Full 2021 List]

Worcester Bosch offers some of the most reliable boilers on the market but they are not immune to the perils of use. Occasionally, you will run into a problem with your boiler, and when this happens, you will need to know how best to handle it.

Fortunately, all Worcester Bosch boilers display error codes that signify what the problem is so that you can get your boiler back up and running in no time.

It is strongly advised to not attempt to fix an issue with your boiler yourself. Instead, reach out to a gas-safe engineer who will know exactly how to handle the issue in a professional and safe manner.

In this article, we have broken down all the Worcester boiler error codes so that you can quickly identify and resolve any issues with your Worcester Bosch boiler.

What are Worcester boiler error codes?

Worcester boiler error codes are the alphanumerical codes displayed on your boiler when there is an issue. This code usually identifies the fault and the cause and will inform a professional gas-safe engineer how best to handle the problem.

Worcester Bosch categorise their boiler error codes into blocking errors, locking errors, fault errors, cause errors, and maintenance codes. The codes are further broken down and vary between models. They are predominantly used by professional gas-safe engineers to identify the problem with the boiler so that they can resolve it.

Worcester Bosch error codes

Let’s first break down the five different types of errors that Worcester Bosch identifies.

Blocking error

When there is a blocking error the boiler will stop operating immediately. However, unlike other faults, the error code will not be displayed. Instead, you will be able to access the cause code by pressing the spanner/return button to identify the cause of the blockage. Once the issue is resolved then the boiler will start operating normally.

Locking error

When there is a locking error, the boiler will display the error code, cause code and flash a warning triangle. After the boiler has been fixed then you will need to press the boiler reset button for 3 seconds to clear the codes.

Fault error

The fault error is an alphanumeric code that will indicate the fault group. This is what will appear on your boiler.

Cause error

The cause error is a three-digit number that is usually found in the information menu. To access this you need to press the spanner/return button on your boiler. The cause code will only appear alongside the fault code when it is a locking error. Other than that, you will always be able to view it in the information menu.

Maintenance code

The maintenance code is easily recognisable as it starts with the letter ‘H’ and is followed by a number. This fault will not stop your boiler from operating, but does act as a warning and tells you that it needs to be looked at by a qualified engineer.

How to reset a Worcester boiler

On occasion, resetting your Worcester boiler can resolve the problem. In most cases, the quickest and easiest way to resolve any boiler issue is to contact a gas-safe engineer. However, before you hire them out to your home, they may suggest that you try resetting your boiler yourself first.

Depending on the model of your boiler there are two different ways to do this. There will either be a clear ‘reset’ button that you press down for 3 seconds. Or there will be a light at the end of the temperature dial which you turn down until it reaches this ‘reset’ point, hold it here for 3 seconds. Remember to turn it back on afterward to see if it has resolved the issue.

Your engineer will let you know if this is an advisable course of action. It is important that you do not reset your Worcester Bosch boiler if it is displaying an EA error code.

Worcester boiler EA error code

If your Worcester boiler is displaying an EA error code this means that the flame is not detected. If you have a gas-operated boiler you need the flame to heat the water in your boiler for central heating and hot water. It is not uncommon to see an EA error code alongside a flashing blue light, again this signifies that there is an issue with the flame.

There are several different reasons why your boiler is displaying the EA error code. There could be little or no gas supply to the boiler, a faulty ignition electrode or lead, or even an issue with the flame sensor. Regardless, it is important to call a qualified gas-safe engineer to handle this problem. You must not reset your Worcester boiler if you see this EA error code as it could cause further damage to your boiler.

Greenstar 8000 error codes

This includes the Greenstar 8000 Life & Style Combi boiler, Greenstar 8000 Life System boiler, Greenstar 8000 Style System, and the Greenstar 8000 Life Regular boiler.

Fault CodeProblem description
200 OBoiler in heating mode
201 OBoiler in hot water mode
202 OBoiler in anti-cycle mode
203 0Boiler on standby – no heat energy demand
204 OCurrent primary water temperature higher than the set value
208 0Chimney sweep demand
224 VSafety temperature limiter has tripped – top-up water until the reset pressure is reached
227 VNo flame signal after ignition – burner control unit could need replacing
228 VFlame signal without flame present – air/gas ratio control valve or ionisation cable may need replacing
305 0Boiler in hot water anti-cycle mode
306 VFlame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
360 VIncompatible code plug – check if a correct code plug is installed and exchange or reconnect code plug
815 W/BLow loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage
1010 ONo 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 WWater pressure too low – the water needs topping up and the vent system or pressure sensor may need replacing
1021 BThe hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected
1022 BHot 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 WThe outside temperature sensor is defective – check the connecting lead
1065 BPressure sensor defective or not connected – check pressure sensor connection as it may need replacing
1068 WOutside temperature sensor defective – check the connecting lead
1073 WShort circuit of the flow temperature sensor – the temperature sensor may need replacing
1074 WNo signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or temperature sensor could need replacing
1075 WShort circuit of the temperature sensor at the heating block – temperature sensor may need replacing
1076 WNo signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead, or the control unit
2920 VError with the flame monitoring
2924 VNo feedback from the modulating gas valve. The gas valve relay is defective – press the reset button and apply burner start, wait to see if fault reoccurs, if it does the gas valve needs replacing
2925 VFeedback from the modulating gas valve is too low
2927 BFlame failed during burner operation. Open the main shut off valve, shut down the appliance and check the gas line, replace the ionisation electrode, set burner correctly and minimum rated load, check the integrity flue system and if the interconnected room air supply is too small, or the size of the ventilation opening is too small, clean the heating block on the flue gas side or replace the control unit/burner control unit
2946 VIncorrect code plug detected – the code plug needs replacing
2948 BNo flame signal. With low output, the burner starts automatically after cleaning. If the fault occurs repeatedly, the setting of the CO2 valves need checking
2950 BNo flame signal. Following starting the procedure the burner starts automatically. After cleaning set the correct gas/air ratio correctly
2963 BThe signal from the flow and heat exchanger temperature sensor is outside the permissible range – the connecting lead needs to connect correctly
2964 BThe flow rate in the heat exchanger is too low
2965 BThe flow temperature is too high
2966 BFlow temperature rise in heat exchanger is too rapid
2967 BFlow/heat exchanger temperature sensor differential is too great
2970 BPressure drop in the heating system is too rapid
2971 BSystem 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 replace the pressure sensor

Greenstar CDi Highflow error codes

Fault CodeDescription
A1Pump is dry or running with air in the system – check system pressure
A5Tank negative thermistor coefficient (NTC) defect
A7Domestic hot water (DHW) negative thermistor coefficient (NTC) defect
A8Energy Management System (EMS) communication error
B1Code plug not detected
B2, B3, B4, B5, B6Data error
B7Burner control error
C6Fan defect
D3External temperature limiter
D5Condensate pump failure
D6Internal heat bank overflow
EAFlame not detected – contact a Gas Safe engineer
E2Primary negative thermistor coefficient (NTC) defect
E9Safety temperature limiter in central heating (CH) flow stat tripped
F0Internal error
F1ROM fault
F7Flame detected after the appliance has been shut off
FAFlame detected after gas shut off
FDReset button pressed – try pressing the reset button again

Greenstar CDi Compact error codes

Fault CodeDescription
T1Ignition test – checking the igniter spark
T2Fan test – checking the basic fan
T3Pump test – checking the basic pump
T4Three-way valve test
T6Ionisation oscillator test
9A 362Error – incorrect HCM fitted
9U 233Heat Control Module (HCM) error – problem with code plug
B7 257Internal error – possible control board problem
C6 215Fan problem – fan is running too fast
C7 214Fan problem – fan is not running
D1 240Return sensor error – sensor may be wet or damaged
E2 222Flow sensor short circuit error
E5 218Flow temperature is too high
E9 219Safety sensor fault – temperature is too high, sensor short circuit or open circuit
EA 227No flame detected or flame signal loss during operation-contact a Gas Safe engineer
F0 237Internal error
F7 228Flame error – false flame or flame detected before burner started
FA 306False flame fault – flame detected after the burner has stopped
FD 231Mains power fault – electrical power interruption
FA 364Gas valve EV2 leak test failed – gas valve leak
FB 365Gas valve EV1 leak test failed
A1 281Pump stuck or running with air in the system
C1 264Airflow stopped during the operation
C4 273Airflow present during last 24 hours
D1 240Return sensor short circuit
D4 271The temperature difference between flow and safety sensor exceeds the limit
E9 224Max thermostat activated – flue gas thermostat overheat
EA 227No ionisation is detected after ignition
EF 349Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212Safety or flow temperature is rising too fast

Greenstar CDi Classic Regular error codes

Fault CodeDescription
B1Code plug not detected
C6Fan speed too low
E2Central heating (CH) flow negative thermistor coefficient (NTC) sensor defective
E9Safety temperature limiter in central heating (CH) flow has tripped
EAFlame not detected -contact a Gas Safe engineer
F0Internal error
F7Flame detected even though appliance is switched off
FAFlame detected after gas shut off
FDThe reset button pressed by mistake

Greenstar CDi Fi Regular error codes

Fault codeDescription
b1Code plug is not detected
C6Fan speed is too low
E9Safety temperature limiter in CH flow has tripped
EAFlame not detected – contact a Gas Safe engineer
F0Internal error
F7Flame detected even though the boiler is switched off
FAFlame detected after gas shut off
FDThe reset button pressed by mistake

Greenstar i System 27/30 error codes

Fault CodeDescription
T1Ignition test – checking the igniter spark
T2Fan test – checking the basic fan
T3Pump test – checking the basic pump
T4Three-way valve test
T6Ionisation oscillator test
9A 362Error – incorrect HCM fitted
9U 233Heat Control Module (HCM) error – problem with code plug
B7 257Internal error – possible control board problem
C6 215Fan problem – fan running too fast
C7 214Fan problem – fan not running
D1 240Return sensor error – sensor may be wet or damaged
E2 222Flow sensor short circuit error
E5 218Flow temperature too high
E9 219Safety sensor fault – temperature too high, sensor short circuit or open circuit
EA 227No flame detected or flame signal loss during operation
F0 237Internal error
F7 228Flame error – false flame or flame detected before burner started
FA 306False flame fault – flame detected after the burner stopped
FD 231Mains power fault – electrical power interruption
FA 364Gas valve EV2 leak test failed – gas valve leak
FB 365Gas valve EV1 leak test failed
A1 281Pump stuck or running with air in the system
C1 264Airflow stopped during the operation
C4 273Airflow present during last 24 hours
D1 240Return sensor short circuit
D4 271The temperature difference between flow and safety sensor exceeds the limit
E9 224Max thermostat activated – flue gas thermostat overheat
EA 227No ionisation detected after ignition
EF 349Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212Safety or flow temperature rising too fast

Greenstar i Combi and System 9/24 boiler error codes

Fault CodeDescription
226The service tool has been connected in the blocking error history menu
FD 231The power has been interrupted during a lockout
C7 214The fan does not run during the start-up phase – the fan harness connector needs checking
C6 215Fan speed too high – check the fan harness and connector
C7 216Fan speed too low – check the fan harness and connector
C7 217The fan has stopped during appliance operation
C1 264The fan stopped during the operation
C4 273Continuous fan operation for the last 24 hours – appliance temporarily blocked
E2 222Flow temperature sensor shorted
E2 233Flow temperature sensor disconnected
E9 276Primary flow temperature exceeded 95°c
E2 350Flow temperature sensor shorted
E2 351Flow temperature sensor disconnected
FA 306Ionisation detected after the gas valve closed
EA 227No ionisation detected after ignition
F7 228Ionisation current detected before burner start
EA 229Loss of ionisation signal during operation
EA 261Heat control module (HCM) potentially defective – reset the appliance
9U 233The control box or heat control module (HCM) is defective or loose, the HCM needs to be checked
C4 237The control box or heat control module (HCM) is defective
F0 238Gas valve or control box error – gas valve coils need checking
F0 239Control box or the heat control module (HCM) is defective – the control box connections need to be checked
F0 242Control box or the heat control module (HCM) is defective – the HCM and control box connections need to be checked
B7 257Control box or the heat control module HCM) is defective- the HCM and control box connections need to be checked
F0 258Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
EH 258Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F1 259Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F0 262Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
F1 263Control box or the heat control module (HCM) is defective – HCM or control box connections needs to be checked
F0 272Control box or the heat control module (HCM) is defective – control box and connections need checking or HCM might not be inserted properly and needs replacing
F0 280Control box or the heat control module (HCM) is defective – control box and connections need checking or HCM might not be inserted properly and needs replacing
F0 290The control box is defective – HCM needs checking as it might not be inserted properly or needs replacing
328Internal error with the mains voltage – frequency may be inconsistent
235Incompatible heat control module (HCM) software versions – control box needs the latest software
356Low mains voltage – the voltage may be interrupted or inconsistent and needs checking
360Heat control module (HCM) invalid – the inserted HCM does not correspond with the control box
A8 362Low mains voltage – the voltage may be interrupted, inconsistent, or heat control module (HCM) invalid
CC 800Outdoor sensor defect available when the accessory outdoor sensor is connected
A1 281Pump stock or running dry
E9 224Flue or high limit thermostat activated
D4 341Primary flow temperature rising too fast

Greenstar Heatslave 11 error codes

Fault CodeDescription
E9210Maximum temperature thermostat or air pressure switch activated. Reset overheat thermostat or air pressure switch before resetting the boiler
E5218Flow temperature too high
E9219, 220 or 221Safety temperature too high, safety sensor short circuit or safety sensor open circuit
E2222, 223 or 233Flow sensor short circuit, flow sensor open circuit, or heat control module code plug missing or defective
F0237 or 238Software relay error – Resistors between plus X4 pins 3 & 5 disconnected or water in the burner control box
F0239 or 259Watchdog relay error or A/D reference relay error – If the error persists, change the control board
F0263Appliance powered off with locking fault present – press reset button to clear
D4271The temperature difference between flow and safety sensors exceeds the limit
E9276 or 277Flow temperature or safety temperature exceeds 95°C
F0278, 279 or 290Sensor test error, A/D convertor error, or A/D convertor reference error
E5332Primary flow has exceeded 105°C – primary sensor overheated
9A360Incorrect HCM for boiler variant – replace with correct HCM
A7808DHW sensor defective – check and replace defect sensor as necessary
A0809Thermal store sensor defective – check and replace defect sensor as necessary
9F855 or 856Burner lockout or 5 burner lockouts repeated resets. Check the burner and fuel supply, and ensure the oil supply is free of contaminants. After five 855 burner lockouts, code 856 is displayed.
H29Warning triangle and house symbol displayed on the controller – weather compensation activated but no weather sensor detected.
H27Warning triangle symbol displayed on the controller – DCW in sensor defect

Greenstar Ri error codes

Including the Greenstar Ri 9/24 and the 27/30.

Fault CodeDescription
No lightNo power at the control board
Light onAppliance on but not operating during demand
Slow flash (mostly off flashes on)Ignition lockout
Slow flash (mostly on flashes off)Flue overheat or heat exchanger overheat
Fast flashVolatile lockout sensor fan or code plug
2 pulsesCheck service mode switch is in minimum position
5 pulsesCheck service mode switch is in max position

GB162 error codes

Fault codeDescription
208The boiler is currently in chimney sweep mode.
200The boiler is in heating mode.
201The boiler is in domestic hot water (DHW) mode.
202The boiler is waiting – there was a heat demand from the on-off or modulating control.
203The boiler is on standby.
204The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature.
212The temperature recorded by the flow temperature sensor or the safety sensor is rising too quickly.
260The flow temperature sensor is not detecting a rise in temperature following a burner start.
265The boiler is waiting in response to a heat demand – the boiler regularly switches to partial load.
268The boiler is in a component test phase.
270The boiler is modulating upwards.
283The boiler is preparing for a burner start – the fan and pump are activated.
284The gas valve has switched.
305The boiler is waiting for domestic hot water (DHW) operation to end


9A 361
The burner control unit that has been fitted is not compatible with the KIM (boiler identification module).
A3 317There is a short circuit in the flue gas temperature sensor contacts.
C6 216The fan speed is too low.
CE 207The water pressure is too low.
CE 266The pump test failed.
D1 241The contacts of the boiler return temperature sensor have been interrupted.
D3 232The external switching contact has opened.
D4 213The actual temperature recorded by the flow temperature sensor or return temperature sensor is rising too quickly.
D4 286The boiler return temperature sensor has detected a return temperature higher than 105°c.
E2 223The flow temperature sensor contacts have been interrupted.
E9 210The temperature measured by the flue gas sensor is too high and is open.
E9 220The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c.
E9 277The safety temperature sensor has measured temperature in excess of 95°c.
E9 285The boiler return temperature sensor has measured a temperature higher than 95°c.
E9 318The flue gas temperature sensor contacts have been interrupted.
EA 234The contacts of the gas valve have been interrupted.
EA 269The ignition device has been activated for too long.
GB162The ignition device has been activated for too long.
F0 278The sensor test has failed – cabling and plug sensors need checking.
F0 279The burner control unit, or KIM, is faulty – the control unit may need replacing.
F0 287The burner control unit, or KIM, has an error.
F7 328A brief power failure has occurred.
EC 256The burner control unit has an error.
H07The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode.
rEThe boiler resets.

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