Worcester boiler fault codes

Boiler Fault Codes 

Fault Codes

Worcester Boiler Fault Codes

Any boiler, whether a Worcester, Vaillant, Baxi, Potterton, Viessmann, Ideal or other brand, will often show you a fault code, usually made up of letters and numbers, such as E28 for example.

These fault codes are there to help our engineers locate the problem in a timely and efficient manner. Very often a single code may have several implications which our team can decipher, and repairs can be put underway.

The temptation is often to Google the code and try to solve the issue without ever calling an engineer. This can be both dangerous and costly. Our dedicated team of highly trained professional engineers has years of experience. Please note, it is actually illegal to work on a gas appliance without the relevant qualifications.

Below is a list of possible Worcester boiler fault codes that ALL require an engineer to visit.

Boiler error codes

CDI Classic Combi

CDI Highflow Combi

CDi Compact

Greenstar 25/30 Si Combi

Greenstar 27/30 I System Boilers

CDi Classic Regular

Greenstar I System or Combi

GB162 Commercial Boiler

Worcester boiler fault codes If you are unsure please don’t hesitate to speak to one of our team. 

Worcester boiler fault codes

CDI Classic Combi

Fault Description
System Behaviour
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
A7The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads 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
A7The hot water negative thermistor coefficient (NTC) sensor is defective – the hot water sensor or connecting leads need checking
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 Highflow Combi

Fault Description
System Behaviour
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
B2, B3, B4, B5, 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

Flame detected after appliance has been shut off


Flame detected after gas shut off


Reset button pressed – try pressing the reset button again

Worcester Bosch CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system Boiler Error Codes

Worcester Bosch boiler fault codes and error codes 

Fault Description
System Behaviour
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 starter
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
FA 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 hours
D1 240Return sensor short circuit
D4 271Temperature difference between flow and safety sensor exceeds limit
E9 224Max thermostat activated – flue gas thermostat overheat
EA 277No 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