Updated on 10th November, 2022 by Martin Astley

Although Worcester Bosch boilers are of high quality, problems can start to present themselves as with any boiler. Some issues are more common than others when it comes to Worcester Bosch boiler error codes. So it’s worth knowing how to identify these (and find solutions for them) in advance.

You can find some of the common Worcester Bosch boiler error codes, along with their solutions below.

1. CDI Classic Combi / CDI Highflow Combi Boiler Error Codes

2. Worcester Bosch CDI Compact / Greenstar 27/30 I System / Greenstar 25/30 SI Combi Boiler Error Codes

T1
T2
T3
T4
T6
9A-362
C6-215
EA-227
F7 228
FB 364
FB 365
A1 281
EF 349
NO CODE 212

3. Worcester Bosch CDI Classic Regular Boiler Error Codes

1. CDI Classic Combi / CDI Highflow Combi Boiler Error Codes

cdi classic and highflow combi boiler error codes

Fault Code	System Behavior	Solution
A1	Either water is leaking or the pump needs freeing or replacing due to the pump running dry.	The best course of action is to bleed your radiators and check your boiler pressure. If the fault code is still showing once you’ve done so, contact Worcester Bosch so someone can take a further inspection.
A7	The hot water negative thermistor coefficient (NTC) sensor is defective – the connecting leads or hot water sensor need checking.	Please contact Worcester Bosch so someone can take a further inspection.
A8	There has been a break in communication with FX sensor controls. Therefore your electrical connections need checking.	Please contact Worcester Bosch so someone can take a further inspection.
B1	Code plug not detected	Reset the boiler
C6	This means that the fan speed is too low.	The fan lead and connector needs an inspection and possibly replacing. Please contact Worcester Bosch for a further inspection.
E2	This means that there is a problem with the central heating. The (NTC) sensor might also be defective.	Please contact Worcester Bosch so someone can take a further inspection.
E9	This means there could be an issue with the system pressure as the safety temperature limiter in the central heating flow has been tripped.	If you still see the fault after you’ve pressed ‘reset’ please contact Worcester Bosch for a further inspection
EA	There is a problem regarding flame loss.	First, you should examine if other gas appliances in your home are working normally so that you know for sure if there is a gas supply in the property. It’s worth checking that the gas supply is on at the meter, if the boiler still doesn’t turn on – then contact Worcester Bosch.
F0	This fault code symbolises an internal error within the boiler system.	If the fault is still showing after you’ve pressed ‘reset’ please contact Worcester Bosch to get a further inspection.
F7	A flame has been detected, although the appliance is not on.	Don’t be tempted to reset your boiler, instead, contact Worcester Bosch for a further inspection.
FA	A flame has been detected even after the gas was shut off.	The gas valve needs checking. Please contact Worcester Bosch to get a further inspection.
FD	The ‘reset’ button has been pressed accidentally.	Try pressing the ‘reset button again to fix this. However, if the problem persists, contact Worcester Bosch to get a further inspection.

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2. Worcester Bosch CDI Compact / Greenstar 27/30 I System / Greenstar 25/30 SI Combi Boiler Error Codes

worcester bosch cdi compact greenstar 2730i and system greenstar 2530si combi boiler error codes

Fault Code	System Behavior	Solution
T1	The boiler is undertaking an ignition test and is thus in test mode.	The boiler normally returns to normal operation once complete. If the problem persists, please contact Worcester Bosch for a further inspection.
T2	The boiler is undertaking a fan test and is thus in test mode.	The boiler typically returns to normal operation once complete. If not, please contact Worcester Bosch for a further inspection.
T3	The boiler is undertaking a pump test and is thus in test mode.	The boiler typically returns to normal operation once complete. If not, please contact Worcester Bosch for a further inspection.
T4	The boiler is undertaking a three-way valve test and is thus in test mode.	The boiler typically returns to normal operation once complete. If not, please contact Worcester Bosch to get a further inspection.
T6	The boiler is undertaking an ionisation oscillator test and is thus in test mode.	The boiler usually returns to normal operation once complete. If the issue persists, please contact Worcester Bosch to get a further inspection.
9A 362	An incorrect Heat Control Module (HCM) was installed.	Please contact Worcester Bosch to get a further inspection.
C6 215	The fan speed is too high.	Turn the boiler’s power off and on again. Once you’ve done this, if your boiler still doesn’t operate correctly, then contact Worcester Bosch.
EA 227	1.) No flame has been detected. There could be an issue with the gas valve and may need adjusting or replacing. 2.) Another reason is there could be a blockage in the siphon or the condensate discharge, check not frozen or blocked. 3.) There may also be damage to the ignition or electrode lead; a flame can’t be made without them. 4.) It could also be an internal leak onto an electrical component.	Unfortunately, you cannot fix this yourself, so please contact Worcester Bosch for an engineer’s help. If you spot a leak, turn off your boiler and contact Worcester Bosch to get the components replaced.
F7 228	There is a flame error.	You should try and reset the system, but contact Worcester Bosch for a further inspection if the issue persists.
FA 364	There is a gas valve leak.	Turn off your boiler and contact Worcester Bosch to send out an engineer.
FB 365	This means there is a gas valve leak.	Turn off your boiler and contact Worcester Bosch to send out an engineer.
A1 281	The pump is running with air in the system or stuck.	Reset your boiler but if the issue persists, contact Worcester Bosch for an engineer’s help.
EF 349	The boiler’s operation is at a minimum burner load.	Make sure the system pressure is between 1 and 1.5 bar. If the issue persists, then contact Worcester Bosch.
NO CODE 212	This means the safety or flow temperature is rising too fast.	Reset your boiler but if the error continues then contact Worcester Bosch for an engineer.

3. Worcester Bosch CDI Classic Regular Boiler Error Codes

worcester bosch cdi classic regular boiler error codes

Fault Code	System Behavior	Solution
B1	Code plug was not detected	If the fault still shows after you’ve pressed ‘reset’, contact Worcester Bosch for a further inspection.
C6	Fan speed is too low	The fan lead and connector need inspection and possibly replacing. Please contact Worcester Bosch for a further inspection.
E2	The central heating (CH) flow negative thermistor coefficient (NTC) sensor is not working properly.	Please contact Worcester Bosch so someone can do a further inspection.
E9	The safety temperature limiter in central heating (CH) flow tripped	If the fault remains after you’ve pressed ‘reset’, contact Worcester Bosch for a further inspection.
EA	Flame not detected	You should examine if other gas appliances in your home are working normally, that way you’ll be certain if there is a gas supply in the property. Check if the gas supply is on at the meter, but if the boiler still doesn’t turn on, contact Worcester Bosch.
F0	Internal error	If the fault remains after you’ve pressed ‘reset, contact Worcester Bosch for a further inspection.
F7	Flame detected although the appliance is off	Don’t try to reset your boiler. Contact Worcester Bosch for a further inspection instead.
FA	Flame detected after gas shut off	The gas valve needs checking. You won’t be able to fix this problem so please contact Worcester Bosch for a further inspection.
FD	The reset button was pressed by mistake	Press the ‘reset’ button again. If the problem continues, contact Worcester Bosch for a further inspection.

4. Worcester Bosch Greenstar I System / Combi Boiler Error Codes

worcester bosch greenstar i system and combi boiler error codes

Fault Code	System Behavior	Solution
226	The service tool is connected in the blocking error history menu	Try and reset your boiler, if the error remains, then contact Worcester Bosch for an engineer’s help.
FD 231	The power got interrupted during a lockout	Reset the boiler
C7 214	The fan does not run during the start-up phase – the fan’s harness connector should be checked	Defective fan – call a boiler engineer
C6 215	Fan speed is too high – check the fan harness and connector	Reset the boiler
C7 216	Fan speed is too low – check the fan harness and connector	Reset the boiler
C7 217	The fan has stopped during appliance operation	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s help.
C1 264	The fan stopped during operation	Reset the boiler. If the fault remains, call a boiler engineer.
C4 273	Due to continuous fan operation for 24 hours, the appliance is temporarily blocked	It will shut off to protect the fan.
E2 222	The flow temperature sensor has shorted	Call a boiler engineer.
E2 233	The flow temperature sensor is disconnected	Call a boiler engineer.
E9 276	Primary flow temperature exceeded 95°C	Check that the pressure is between 1.0 and 1.5 bar. Try to reset the boiler, but contact Worcester Bosch for an engineer’s help if the issue persists.
E2 350	The flow temperature sensor has shorted	Check that the pressure is between 1.0 and 1.5 bar. Try to reset the boiler but if the issue persists, then contact Worcester Bosch for an engineer’s help.
E2 351	The flow temperature sensor is disconnected	Check that pressure is between 1.0 and 1.5 bar. Try to reset the boiler. If the issue persists, then contact Worcester Bosch for an engineer’s help.
FA 306	Ionisation was detected after the gas valve closed	Try to reset your boiler but if it doesn’t reset then contact Worcester Bosch.
EA 227	No ionisation was detected after ignition	Please contact Worcester Bosch to get an engineer’s help. If you spot a leak, turn off your boiler and contact Worcester Bosch to get the components replaced.
F7 228	Isioniation current detected before burner start	The best course of action is to reset the system, but please contact Worcester Bosch to further inspect if the issue persists.
EA 229	Loss of ionisation signal during operation	Check the pressure is between 1.0 and 1.5 bar. Try to reset the boiler. If the issue persists, then contact Worcester Bosch for an engineer’s assistance.
EA 261	The heat control module (HCM) is potentially defective – reset the appliance	Reset the boiler but if the issue remains, you will need to call a boiler engineer.
9U 233	The control box or heat control module (HCM) is either loose or defective, the HCM needs to be checked	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s help.
C4 237	The heat control module (HCM) or control box is defective	Call a boiler engineer.
F0 238	Gas valve or control box error – check the gas valve coils	Double-check that the system pressure is between 1.0 and 1.5 bar. Also, check whether other gas appliances are working as normal, to confirm that your gas supply is present. If you’ve done this and your boiler still isn’t operating correctly, then contact Worcester Bosch.
F0 239	The control box or the heat control module (HCM) is defective – the control box connections should be checked	This may be an electrical issue, so please contact Worcester Bosch for an engineer’s help.
F0 242	The control box or the heat control module (HCM) is defective – the HCM and control box connections should be checked	This may be an electrical issue, so please contact Worcester Bosch for an engineer’s help.
B7 257	Control box or the heat control module HCM) is defective- the HCM and control box connections should be checked	Please contact Worcester Bosch for a further inspection.
F0 258	Control box or the heat control module (HCM) is defective – HCM or control box connections should be checked	This isn’t something you can fix. Contact Worcester Bosch for an engineer’s assistance.
EH 258	Control box or the heat control module (HCM) is defective – HCM or control box connections should be checked	This isn’t something you can fix. Contact Worcester Bosch for an engineer’s assistance.
F1 259	Control box or the heat control module (HCM) is defective – HCM or control box connections should be checked	This isn’t something you can fix. Contact Worcester Bosch for an engineer’s assistance.
F0 262	Control box or the heat control module (HCM) is defective – HCM or control box connections should be checked	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
F1 263	Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
F0 272	Control 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	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
F0 280	Control 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	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
F0 290	Control 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	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
328	Control 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	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
235	Incompatible heat control module (HCM) software versions – control box needs the latest software	Please contact Worcester Bosch for an engineer’s assistance.
356	Low mains voltage – the voltage may be interrupted or inconsistent so it should be checked	This may require an electrician if it’s an issue with your house mains
360	Heat control module (HCM) invalid – the inserted HCM does not correspond with the control box	Please contact Worcester Bosch for an engineer’s assistance.
A8 362	Low mains voltage – the voltage may be interrupted, inconsistent or heat control module (HCM) invalid	This may require an electrician if it’s an issue with your house mains
CC 800	Outdoor sensor defect available when an accessory outdoor sensor is connected	Please contact Worcester Bosch for an engineer’s assistance.
A1 281	Pump stock or running dry	Try to reset your boiler. If the issue persists, contact Worcester Bosch to send out an engineer.
E9 224	Flue or high limit thermostat activated	Try to reset your boiler. If the issue persists then contact Worcester Bosch for a boiler’s assistance.
D4 341	Primary flow temperature rising too fast	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.

5. Worcester Bosch GB162 Boiler Error Codes

worcester bosch gb162 boiler error codes

Fault Code	System Behavior	Solution
208	The boiler is in chimney sweep mode	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
200	The boiler is in heating mode	Please contact Worcester Bosch for an engineer’s assistance.
201	The boiler is currently in domestic hot water (DHW) mode	Please contact Worcester Bosch for an engineer’s assistance.
202	The boiler is waiting – there was a heat demand from the modulating or on-off control	Please contact Worcester Bosch for an engineer’s assistance.
203	The boiler is on standby	Please contact Worcester Bosch for an engineer’s assistance.
204	The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature	Please contact Worcester Bosch for an engineer’s assistance.
212	The temperature recorded by the safety or flow temperature sensor is rising too rapidly.	Please contact Worcester Bosch for an engineer’s assistance.
226	The diagnosis tool was connected and is now locked out	Please contact Worcester Bosch for an engineer’s assistance.
260	The flow temperature sensor doesn’t detect a rise in temperature after a burner start	Please contact Worcester Bosch for an engineer’s assistance.
265	The boiler is waiting in response to a heat demand – it switches regularly to partial load	Please contact Worcester Bosch for an engineer’s assistance.
268	Component test phase	Please contact Worcester Bosch for an engineer’s assistance.
270	The boiler is modulating upwards	Please contact Worcester Bosch for an engineer’s assistance.
283	The boiler is getting prepared for a burner start – the fan and pump are activated	Please contact Worcester Bosch for an engineer’s assistance.
284	The gas valve is switched	Please contact Worcester Bosch for an engineer’s assistance.
305	The boiler is waiting for the domestic hot water (DHW) operation to come to an end	Try to reset the boiler, but contact Worcester Bosch for an engineer’s assistance if the issue persists.
235	The KIM (boiler identification module) is really new for the burner control unit	Please contact Worcester Bosch for an engineer’s assistance.
360	The fitted KIM is not compatible with the burner control unit	Please contact Worcester Bosch for an engineer’s assistance.
9A 361	The fitted burner control unit is not compatible with the KIM (boiler identification module).	Please contact Worcester Bosch for an engineer’s assistance.
9U 233	The control box or heat control module (HCM) is loose or defective.	Please contact Worcester Bosch for an engineer’s assistance.
A3 317	There is a short circuit in the flue gas temperature sensor contacts	Please contact Worcester Bosch for an engineer’s assistance.
B7 257	The burner control unit or the KIM is defective	Please contact Worcester Bosch for an engineer’s assistance.
C1 264	No power supply or control signal to the fan during operation	Please contact Worcester Bosch for an engineer’s assistance.
C4 273	The boiler was switched off for 2 minutes because it had been operating continuously for over 24 hours	Please contact Worcester Bosch for an engineer’s assistance.
C6 215	Fan speed is too high	Please contact Worcester Bosch for an engineer’s assistance.
C6 216	Fan speed is too low	Please contact Worcester Bosch for an engineer’s assistance.
C7 214	The fan does not run during the start phase	Please contact Worcester Bosch for an engineer’s assistance.
C7 217	When starting up, the fan speed is irregular	Reset the boiler or contact Worcester Bosch for an engineer.
CE 207	Water pressure is too low	Try to top up the pressure so that the needle is between 1 and 1.5 bar. If the pressure continues to drop, contact Worcester Bosch as you may have a leak.
CE 266	Pump test failed	Please contact Worcester Bosch for an engineer’s assistance.
D1 240	The boiler return temperature sensor contacts have short-circuited	Please contact Worcester Bosch for an engineer’s assistance.
D1 241	The boiler return temperature sensor contacts have interrupted	Please contact Worcester Bosch for an engineer’s assistance.
D3 232	The external switching contact has opened	Please contact Worcester Bosch for an engineer’s assistance.
D4 213	The actual temperature recorded by the return or flow temperature sensor is rising too quickly	Please contact Worcester Bosch for an engineer’s assistance.
D4 271	The actual temperature difference between flow and safety temperature sensor is too high	Please contact Worcester Bosch for an engineer’s assistance.
D4 286	The boiler return temperature sensor detected a return temperature higher than 105°c	Please contact Worcester Bosch for an engineer’s assistance.
E2 222	There is a short circuit in the flow temperature sensor contacts	Please contact Worcester Bosch for an engineer’s assistance.
E2 223	The flow temperature sensor contacts have been interrupted	Please contact Worcester Bosch for an engineer’s assistance.
E5 218	The temperature captured by the flow temperature sensor is over 105°C	Please contact Worcester Bosch for an engineer’s assistance.
E9 210	The temperature measured by the flue gas sensor is too high and is open.	Please contact Worcester Bosch for an engineer’s assistance.
E9 219	The safety temperature sensor has captured a temperature over 105°C	Please contact Worcester Bosch for an engineer’s assistance.
E9 220	This means the safety temperature sensor contacts have shorted or the safety temperature sensor has detected a temperature above 130°c.	Please contact Worcester Bosch for an engineer’s assistance.
E9 224	The contacts of the safety temperature sensor have been interrupted	Please contact Worcester Bosch for an engineer’s assistance.
E9 276	That the primary flow temperature is over 95°C.	Please contact Worcester Bosch for an engineer’s assistance.
E9 277	The safety temperature sensor has measured temperature over 95°C	Please contact Worcester Bosch for an engineer’s assistance.
E9 285	the boiler return temperature sensor has measured a temperature higher than 95°c	Please contact Worcester Bosch for an engineer’s assistance.
E9 318	The flue gas temperature sensor contacts are interrupted	Please contact Worcester Bosch for an engineer’s assistance.
EA 227	An insufficient ionisation current was measured following ignition of the burner	Unfortunately, this isn’t something you’ll be able to fix yourself, so please contact Worcester Bosch to send out an engineer. If you spot a leak, turn off your boiler and contact Worcester Bosch to get the components replaced.
EA 229	The ionisation current detected during the burning phase was insufficient	Check the pressure is between 1.0 and 1.5 bar. Try to reset the boiler, if the issue still persists, then contact Worcester Bosch for an engineer’s assistance.
EA 234	The gas valve contacts were interrupted	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
EA 261	The burner control unit is faulty	Try to reset the boiler but if the issue remains, then contact Worcester Bosch for an engineer’s assistance.
EA 269	The ignition device has been activated for a long period of time	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
F0 238	The burner control unit KIM is defective.	Double-check to ensure the system pressure is between 1.0 and 1.5 bar. Also check any other gas appliances to see if they are working normally, to confirm that your gas supply is present. If you’ve done this and your boiler still won’t operate correctly, then contact Worcester Bosch.
F0 239	The burner control unit KIM (boiler identification module) has an error. Cabling may have poor contact breaks and pinching or the wiring and plug of the burner control unit need checking, along with the operating characteristics of the boiler by replacing the burner control unit.	This may be an electrical issue, so please contact Worcester Bosch for an engineer’s assistance.
F0 242 – F0 253, and F0 255, F0 259, F0 263, F0 267, F0 272	The burner control unit (KIM) is defective – the wiring of the burner control unit needs to be checked, along with the operating characteristics of the boiler by replacing the burner control unit.	This may be an electrical issue, so please contact Worcester Bosch for an engineer’s assistance.
F0 278	The sensor test failed – plug sensors and cabling need to be checked	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
F0 279	The burner control unit, or KIM, is faulty – the control unit may need replacing	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
F0 280	The burner control unit is faulty	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
F0 287	The burner control unit, or KIM, has some error	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
F0 290	The KIM or burner control unit is defective	Contact Worcester Bosch for an engineer’s assistance.
F7 228	An ionisation current was detected before the burner started	The best thing to do is to try and reset the system, if the issue persists then please contact Worcester Bosch to take a further inspection.
F7 328	A brief power failure has occurred	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
FA 306	An ionisation current was measured after the burner shut off	Try to reset your boiler, if it doesn’t reset then contact Worcester Bosch.
FD 231	The mains voltage was interrupted due to an interlocking fault	Try to reset your boiler, but if the code remains, contact an electrician.
EC 256	The burner control unit has an error	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
EH 258	The burner control unit is faulty – check the plug and wiring.	This isn’t something you’ll be able to fix. Contact Worcester Bosch for an engineer’s assistance.
GB162	The ignition device has been activated for too long.	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
H07	The current water pressure is extremely low which limits the performance in heat mode, along with domestic hot water (DHW) mode	This isn’t something you’ll be able to fix. Please contact Worcester Bosch for an engineer’s assistance.
HrE	The boiler keeps resetting	You need to contact an engineer to fix this problem.
rE	The boiler resets	Wait for the boiler to reset, if the issue persists – then please contact Worcester Bosch for an engineer’s assistance.

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6. Worcester Bosch Greenstar Ri Boiler Faults Codes

worcester bosch greenstar ri boiler faults codes

Fault Code	System Behavior	Solution
No light	There is no power at the control board	Try to reset the boiler, but contact Worcester Bosch for an engineer’s assistance if the issue persists.
Light on	Appliance on but not operating during demand	Try to reset the boiler, but contact Worcester Bosch for an engineer’s help if the issue remains.
Slow flash (mostly off flashes on)	Ignition lockout.	Try to reset your boiler. This can be done by turning the control knob anti-clockwise to reset the position. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
Slow flash (mostly on flashes off)	Flue overheats or heat exchangers overheat.	Try to reset your boiler. This can be done by turning the control knob anti-clockwise to reset the position. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
Fast flash	Volatile lockout sensor fan or code plug	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2 pulses	The check-service mode switch is in minimum position	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
5 pulses	The Check-service mode switch is in the max position.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.

7. Worcester Bosch Greenstar 8000 life Combi Boiler Error Codes

worcester bosch greenstar 8000 life combi boiler error codes

Fault Code	System Behavior	Solution
200 O	The boiler is in heating mode.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
201 O	Boiler in hot water mode.	Try resetting the boiler. This should fix it.
202 O	The boiler is in anti-cycle mode.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
203 0	This means the boiler is on standby – no heat energy demand.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
204 O	The current primary water temperature is higher than the set value.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
208 O	This shows that the boiler is in chimney sweep demand.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
224 V	The safety temperature limiter has tripped.	Try top-up water until the reset pressure is reached. If the issue persists, then contact Worcester Bosch for an engineer’s help.
227 V	There is no flame signal after the ignition burner. The control unit may need replacing.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
228 V	There is a flame signal without a flame present. The air/gas ratio control valve may need to be replaced.	Try to reset the boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
305 0	The boiler is in hot water anti-cycle mode.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
306 V	There is an issue with the flame signal after the fuel supply is closed. The air/gas ratio control valve may need to be replaced.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
815 W/B	The low loss header temperature sensor is faulty. Check the sensor port or the differential sensor may be installed incorrectly or damaged.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1010 O	There is no BUS communication cable, EMS-Bus isn’t connected or is damaged – connect the cable for the EMS-Bus or replace the damaged cable exchange fuse.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1017 W	The water pressure is too low – the water needs topping up and the pressure sensor or vent system could need replacing.	Try topping up your pressure. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1021 B	The hot water temperature sensor is faulty – the plug to the hot water temperature sensor may be disconnected..	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1022 B	The hot water storage temperature sensor does not work.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1037 W	The outside temperature sensor is not working – check the connecting lead.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1065 B	The pressure sensor is not connected or defective – check the pressure sensor connection because it may need to be replaced..	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1068 W	The outside temperature sensor does not work – check the connecting lead.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1073 W	The temperature sensor may need replacing.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1074 W	No signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or the temperature sensor might need to be replaced.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1075 W	Short circuit of the temperature sensor at the heating block – temperature sensor may need replacing.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
1076 W	There is no signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead or the control unit.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2920 V	Error with the flame monitoring.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2924 V	No feedback from the modulating gas valve. The gas valve relay is defective.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2925 V	Feedback from the modulating gas valve is too low.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2927 B	The flame failed during the burner operation.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2946 V	The incorrect code plug has been detected – it needs replacing.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2948 B	There is no flame signal. If the fault occurs, again and again, the setting of the CO2 valves need to be checked.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2950 B	There is no flame signal.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2963 B	The signal from the heat exchanger and the flow temperature sensor is outside of range.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2964 B	The flow rate in the heat exchanger is too low.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2965 B	The flow temperature is too high.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
966 B	The flow temperature rise in the heat exchanger is very rapid.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2967 B	The heat/flow exchanger temperature sensor differential is too great.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2970 B	The pressure drop in the heating system is too fast.	Try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.
2971 B	The system pressure is too low – the heating system needs venting or water needs topping up until the preset pressure is reached.	To fix, replace the cable to the pressure sensor and replace the pressure sensor. Otherwise, try to reset your boiler. If this does not fix the problem then contact Worcester Bosch for an engineer’s help.

Frequently Asked Questions (FAQs)

Why is my Worcester Boiler Flashing?

There are three kinds of lights on the Worcester boiler and each one indicates something different. The green light, for instance, typically indicates that the burner is operating properly, which means it is a good sign. However, sometimes even with the boiler working fine, the green light can go off. There are reasons for this, for instance, LED or PCB failure, mainly the things that power the light on the boiler’s panel. The blue light indicates that the boiler has power going to it. There may be reasons why the blue light is not showing; for instance, LED and PCB failure. Additionally, it could also point to socket failure – it is worth checking a few of the appliances with the same socket the boiler is usually plugged into in the house and see if they are working okay.

What do the symbols mean on a Worcester Boiler?

Many symbols might appear on the Worcester boiler. If your Worcester Bosch boiler is flashing a symbol you don’t recognise. It might be one of the following:

Siphon fill mode. The boiler runs at a low burn for around 15 minutes to fill the condense trap. This happens once the boiler is turned off, if it has not been used for a day or more, and if the control knob has been turned down and back up. This is a perfectly normal symbol- it is a safety feature. It will last about 15 minutes, then the boiler will go back to normal.
Key Lock (or child lock) – this is when the front panel of the boiler has been locked (New Greenstar 24/28 only)
One key has been pressed
Two keys have been pressed at the same time
The SE Code is not a fault but it’s a function that is displayed when the boiler has run for 2324 hours, which is about 12 months. Therefore, it is due for a service.

Why is my Boiler Flashing EA?

The EA fault code indicates the need for activation of a safety device to prevent any gas from being let out when the boiler has failed to light.

What does U2 mean on a Worcester Boiler?

This code means that the boiler flow temperature is too high and the boiler will shut down until it has cooled down.

What does the Worcester Bosch fault code U9 mean?

U9 means the temperature is 109 degrees as measured inside the boiler. The boiler has massively overheated. This is either due to a faulty pump not working, a restriction in the plate heat exchanger or a faulty PCB not sending power to the pump.