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2021 Worcester Bosch Boiler Error & Fault Codes


The Worcester Bosch Error Codes are an indicator for identifying the fault within your boiler and what needs to be done for fixing it. When you hear a beeping noise from your Worcester Bosch boiler and you see these error codes on your display; this is a clear indication that something is wrong with your boiler and you need to call a Worcester Bosch engineer immediately.

Error codes on your boiler can be a little bit daunting to diagnose and fix. There are a number of codes and many different error conditions that can arise, which means you could end up chasing your tail for a while. A code is triggered when there is some kind of fault inside the Worcester Bosch or something has gone wrong with the boiler, such as: illumination of the pilot light, water temperature is too low or high, it won’t start etc.

Our fault code guide will show you what error codes to look out for when needing to call for help, so your problem with your Worcester Bosch boiler is fixed and restored as soon as possible.

CDI Classic Combi Error Codes


Ever had the problem that your CDI Classic combi boiler is showing what appears to be just random numbers on the display? Don't worry. This is nothing to worry about. Here's a list of the meaning of each error code and whether it's serious or not, so you can make a decision about what action you need to take.

Fault Code Possible Cause
A1Water is leaking or the pump needs replacing or freeing due to the pump running dry.
A7The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads need checking.
A8Break communication to FX sensor controls electrical connections need checking.
B1Code plug not detected .
C6Fan speed too low – the fan lead and connector need checking and may need replacing.
E2Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.
E9Safety temperature limiter in central heating (CH) flow has tripped the system pressure or safety temperature limiter needs checking.
EAFlame not detected due to a gas issue – the gas supply, power supply or igniter, electrode and lead need checking – contact a Gas Safe installer.
F0Internal error – electrical connector contacts or programmer interface module – check ignition leads are not loose.
F7Flame detected even though the appliance is switched off – check the electrode assembly is dry and the pcb and flue are clear.
FAFlame detected after gas shut off – the gas valve needs checking – hire a Gas Safe installer.
FDReset button pressed by mistake – press reset button again.

CDI Compact Error Codes


Worn or broken components, problems with burners and pressure issues can each lead to problems with your Compact boiler. To get a list of error codes followed by a detailed description of what is wrong with your boiler, read below.

This table holds the most common boiler error codes from Worcester Bosch's CDI Compact. The model number of the boiler should be present on some form of user guide or service manual.

Fault Code Possible Cause
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 burner stop
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 operation
C4 273Airflow present during last 24 hour
D1 240Return sensor short circuit
D4 271Temperature difference between flow and safety sensor exceeds 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

CDI Highflow Combi Error Codes


CDI Highflow Combi boilers are very common and loved by many. Unfortunately, they have a tendency to develop issues which in some cases can be complex. This is due to how technical they are.

There are a lot of different error codes which can pop up on your screen, so here's a list of the main error codes you may encounter along with what each means.

Fault Code Possible Cause
A1Pump dry run detection or pump is running in air the system pressure needs checking
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
B2Data error
B3Data error
B4Data error
B5Data error
B6Data error
B7Burner control error
C6Fan defect
D3External temperature limiter
D5Condensate pump failure
D6Internal heat bank overflow
EAFlame not detected
E2Primary negative thermistor coefficient (NTC) defect
E9Safety temperature limiter in central heating (CH) flow stat tripped
F0Internal error
F1ROM fault
F7Flame detected after appliance has been shut off
FAFlame detected after gas shut off
FDReset button pressed – try pressing the reset button again

CDI Classic Regular Error Codes


The Worcester Bosch CDI Classic Regular error codes are a list of errors that are displayed when the boiler has an issue within the control unit. It is designed to allow an engineer or service engineer to be able to diagnose the issue and ultimately fix it. This can range from issues such as flashing fault codes (a fault code that flashes on and off on the display screen), continuous fault codes (a fault code that stays on the screen).

The Worcester Bosch CDI Classic range has come a long way since the original design. The most common error is the classic “E” light on your display. That means something is wrong with your burner management system, so let’s take a look at all of the Worcester Bosch CDI Classic Regular boiler error codes and what they mean.

Fault Code Possible Cause
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
F0Internal error
F7Flame detected even though appliance switched off
FAFlame detected after gas shut off
FDReset button pressed by mistake

GB162 Error Codes


Worcester Boiler GB162 error codes can be a real nightmare. Not only do you have to find out the error code you can’t just expect it to be the same every time. There are so many variables and combinations of factors, not to mention the fact that there could well be multiple problems. Having a list of Worcester Bosch error codes handy will make it easy for you to troubleshoot your system and find out exactly what the problem is.

Being able to identify what Worcester Bosch boiler error codes mean is essential if you are having problems. This guide lists all of the GB162 fault codes that you might find.

Fault Code Possible Cause
208The boiler is 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
226Diagnosis tool was connected and is now locked out
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
268Component test phase
270The boiler is modulating upwards
283The boiler is preparing for a burner start – the fan and pump are activated
284The gas valve is switched
305The boiler is waiting for domestic hot water (DHW) operation to end
235The KIM (boiler identification module) is too new for the burner control unit
360The KIM that has been fitted is not compatible with the burner control unit
9A 361The burner control unit that has been fitted is not compatible with the KIM (boiler identification module)
9U 233The burner control unit or KIM (boiler identification module) is faulty
A3 317Short circuit in the flue gas temperature sensor contacts
B7 257The burner control unit or the KIM (boiler identification module) is faulty
C1 264No control signal or power supply to the fan during operation
C4 273The boiler was switched off for a maximum of 2 minutes because it had been operating continuously for more than 24 hours
C6 215The fan speed is too high
C6 216The fan speed is too low
C7 214The fan does not run during the start phase
C7 217The fan speed is irregular when starting up
CE 207Water pressure is too low
CE 266Pump test failed
D1 240The contacts of the boiler return temperature sensor have been short circuited
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 271Actual temperature differential between flow and safety temperature sensor is too high
D4 286The boiler return temperature sensor has detected a return temperature higher than 105°c
E2 222Short circuit in the flow temperature sensor contacts
E2 223The flow temperature sensor contacts have been interrupted
E5 218The temperature captured by the flow temperature sensor exceeded 105°c
E9 210The temperature measured by the flue gas sensor is too high and is open
E9 219The safety temperature sensor has captured a temperature in excess of 105°C
E9 220The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c
E9 224The contacts of the safety temperature sensor have been interrupted
E9 276The temperature flow sensor has measured a temperature in excess of 95°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 227An insufficient ionisation current was measured following ignition of the burner
EA 229The ionisation current detected by the system during the burning phase was insufficient
EA 234The contacts of the gas valve have been interrupted
EA 261The burner control unit is faulty
EA 269The ignition device has been activated for too long
F0 238The burner control unit KIM (boiler identification module) is faulty
F0 239The burner control unit KIM (boiler identification module) has an error. Cabling might have poor contact breaks and pinching or the plug and wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 240The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 241The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 242The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 243The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 244The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 245The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 246The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 247The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 248The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 249The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 250The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 251The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 252The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 253The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 255The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 259The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 263The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 267The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 272The burner control unit (KIM) is faulty – the wiring of the burner control unit needs checking, also check the operating characteristics of the boiler by replacing the burner control unit.
F0 278The sensor test has failed – cabling and plug sensors need checking
F0 279The burner control unit, or KIM, is faulty – control unit may need replacing
F0 280The burner control unit is faulty
F0 287The burner control unit, or KIM, has an error
F0 290The burner control unit, or KIM, is faulty
F7 228An ionisation current was measured before the burner started
F7 328A brief power failure has occurred
FA 306An ionisation current was measured after the burner went out
FD 231The mains voltage was interrupted during an interlocking fault
EC 256The burner control unit has an error
EH 258The burner control unit is faulty – check the plug and wiring of the burner control unit.
H07The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode
HrEThe boiler keeps resetting
rEThe boiler resets

Greenstar 25/30Si Combi Error Codes


The greenstar 25/30Si combi boiler is a popular choice of boiler for many home owners. The comile is an update to the Greenstar 25 and offers much more flexibility when it comes to selecting a programmer that is compatible with your needs. I feel this new model is a huge success as it has offered so many happy homeowners the chance to get economical and efficient heating solutions for their homes.

Greenstar 25/30Si Combi boilers use a series of error codes to tell you when something is wrong with your boiler. Error codes can be frustrating as they make it difficult to identify the problem clearly so this table will help you understand what each error code means.

Fault Code Possible Cause
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 burner stop
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 operation
C4 273Airflow present during last 24 hour
D1 240Return sensor short circuit
D4 271Temperature difference between flow and safety sensor exceeds 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 27/20 System Error Codes


The Worcester Bosch Greenstar 27/20 system has a large number of error codes you could get. Some are more serious than others, however some can be easily rectified with some research and understanding.

These error codes indicate a fault and will display on the unit’s digital screen. You can refer to the table in this article to find an error code and its meaning.  It’s important to know what error code your Greenstar 27/20 System is displaying, so you can remedy the problem. Please note there are a few instances when no code displays on the Greenstar system; these particular instances result from a problem with the control box, wiring, or both.

Fault Code Possible Cause
T1Ignition test – checking the igniter spark
T2Fan test – checking the basic fan
T3Pump test – checking the basic pump
T4 Three 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 burner stop
FD 231Mains power fault – electrical power interruption
FA 364 Gas 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 operation
C4 273Airflow present during last 24 hour
D1 240Return sensor short circuit
D4 271Temperature difference between flow and safety sensor exceeds 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 System Error Codes


All Greenstar I System boilers have a set of error codes built into the system. This list of boiler error codes will help you diagnose any faults that have been encountered on your system. Understanding what has caused the error code means you can attempt to manually reset your boiler, which may clear the issue up. If not, you'll need to call out a registered installer for assistance.

Fault Code Possible Cause
226Service tool has been connected in the blocking error history menu
FD 231The power has been interrupted during a lockout
C7 214Fan does not run during the start up phase – 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 217Fan has stopped during appliance operation
C1 264Fan stopped during 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 228Isioniation current detected before burner start
EA 229Loss of ionisation signal during operation
EA 261Heat control module (HCM) potentially defective – reset the appliance
9U 233Control box or heat control module (HCM) is defective or loose, the HCM needs to be checked
C4 237Control 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 checking
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 need 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 need 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 need replacing
F0 290Control box is defective – HCM needs checking as it might not be inserted properly or need replacing
328Internal error with the mains voltage – frequency may be inconsistent
235Incompatible heat control module (HCM) software versions – control box needs 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 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 8000 Error Codes


Many Greenstar 8000 error codes are generated by faults with sensors or equipment. These include but are not limited to flame failure, pump failure, and obstruction in the flow passages. This guide will help you identify common error codes associated with boiler’s operation that may occur when operating Worcester Bosch Greenstar 8000 boilers.

There are two main boilers in this range, the Greenstar 8000 and Greenstar 8000 eco models. These two models are slightly different, but more or less the same in terms of error codes.

Fault Code Possible Cause
200 OBoiler in heating mode
201 OBoiler in hot water mode
202 OBoiler in anti-cycle mode
203 0Boiler in standby – no heat energy demand
204 OCurrent primary water temperature higher than 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 may need replacing as might the ionisation cable
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 BHot 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 WOutside 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 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 procedure the burner starts automatically. After cleaning set the correct gas / air ratio correctly
2963 BSignal from flow and heat exchanger temperature sensor outside the permissible range – the connecting lead needs connecting correctly
2964 BFlow rate in heat exchanger is too low
2965 BFlow temperature too high
2966 BFlow temperature rise in heat exchanger too rapid
2967 BFlow / heat exchanger temperature sensor differential too great
2970 BPressure drop in heating system too rapid
2971 BSystem pressure 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
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