Worcester Boiler Error Codes, Fault Codes Meanings & Fixes

Worcester boiler error codes and fault codes, what they mean and how to fix them

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 Worcester boiler, and when this happens, you will need to know how best to handle it.

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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. Even the best combi boilers break at some point so let’s see what the problem is.

One way of ensuring your boiler is working at its best is to book a boiler service which you can do online here. This is like an MOT for your Worcester Bosch boiler and is recommended every year by the manufacturer and if there are any Worcester Bosch fault codes showing, you can get them fixed.

Fixing Worcester Bosch boiler problems

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 and save you from having to pay what a new boiler cost for full boiler installation just yet if it is something as simple as a frozen condensate pipe or low boiler pressure.

What are Worcester boiler error codes?

Worcester boiler error codes are the alphanumerical codes displayed on your boiler when there is an issue and can often be picked up early by getting a Worcester Bosch boiler service every year.

This code usually identifies the fault and the cause and will inform a professional Gas Safe engineer on how best to handle the problem. Their new condensing boilers have a nice LCD screen that is really easy to read.

How to know if your Worcester Bosch boiler is faulty?

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. If your boiler isn’t working, they are predominantly used by professional Gas Safe engineers to identify the problem with the boiler so that they can resolve it.

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Worcester Bosch error codes for Greenstar boilers

Let’s first break down the five different types of errors that Worcester Bosch identifies for it Greenstar boiler range. This is one of the most popular boiler ranges on the market so don’t worry if you need this boiler fixing. If your boiler is starting to get old, however, it may be worth upgrading your old Worcester to one of the new Greenstar models.

It could be something as simple as repressurising your Worcester boiler.

Worcester bosch 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.

Worcester bosch 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 Worcester boiler reset button for 3 seconds to clear the codes.

Worcester Bosch 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.

Worcester Bosch 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. This could be something like a boiler water leak or mean that your Worcester boiler needs draining and our central heating system flushing.

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.

Resetting a Worcester Bosch boiler after a fault code

Check the manual, and 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 with flashing blue light

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 a Worcester EA error code alongside a flashing blue light, again this signifies that there is an issue with the flame.

A21 error for faulty thermostat

The Worcester boiler error code A21 means that your thermostat and boiler are not communicating due to a lack of an RF signal. The most common error is A21 and it can be easily fixed without the help of an engineer.

EA 227 error – check for frozen condensate pipe

If you are seeing the very common EA 227 error code and it is freezing outside, then we always suggest checking your condensate pipe. if this has frozen it will cause a blockage and stop the boiler from igniting.

See how to thaw a frozen condensate pipe here.

C6 error

Another unfortunatley popular err is the Worcester C6 fault code which relates to the fan not working properly – Easily fixed but very annoying and can also be linked to frozen condensate pipes too.

Worcester Bosch error codes & what they mean

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.

What do the Worcester boiler symbols look like?

If your Greenstar boiler isn’t working, then there may be some form of symbol displayed on your boiler. Depending on which model you have will depend on which Worcester boiler symbols are showing.

The best way to check is to look at the Worcester manuals either physically or online. Our fault code tables below are probably a quicker way of diagnosing what is wrong with your boiler though and checking if you need a Gas Safe engineer.

Worcester 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 Code	Problem description
200 O	Boiler in heating mode
201 O	Boiler in hot water mode
202 O	Boiler in anti-cycle mode
203 0	Boiler on standby – no heat energy demand
204 O	Current primary water temperature higher than the set value
208 0	Chimney sweep demand
224 V	Safety temperature limiter has tripped – top-up water until the reset pressure is reached
227 V	No flame signal after ignition – burner control unit could need replacing
228 V	Flame signal without flame present – air/gas ratio control valve or ionisation cable may need replacing
305 0	Boiler in hot water anti-cycle mode
306 V	Flame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
360 V	Incompatible code plug – check if a correct code plug is installed and exchange or reconnect code plug
815 W/B	Low loss header temperature sensor faulty – check the sensor port or check the differential sensor for incorrect installation position or breakage
1010 O	No BUS communication cable, EMS-Bus isn’t connected or damaged – connect the cable for the EMS-Bus or replace the damaged cable exchange fuse
1017 W	Water pressure too low – the water needs topping up and the vent system or pressure sensor may need replacing
1021 B	The hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected
1022 B	Hot water storage temperature sensor is defective – connect the plug to the hot water temperature sensor correctly, mount the hot water temperature sensor correctly or replace the hot water temperature sensor
1037 W	The outside temperature sensor is defective – check the connecting lead
1065 B	Pressure sensor defective or not connected – check pressure sensor connection as it may need replacing
1068 W	Outside temperature sensor defective – check the connecting lead
1073 W	Short circuit of the flow temperature sensor – the temperature sensor may need replacing
1074 W	No signal from the flow temperature sensor available – connect the plug to the flow temperature sensor correctly or temperature sensor could need replacing
1075 W	Short circuit of the temperature sensor at the heating block – temperature sensor may need replacing
1076 W	No signal from the temperature sensor at the heating block available – replace the temperature sensor, the connecting lead, or the control unit
2920 V	Error with the flame monitoring
2924 V	No feedback from the modulating gas valve. 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 V	Feedback from the modulating gas valve is too low
2927 B	Flame 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 V	Incorrect code plug detected – the code plug needs replacing
2948 B	No flame signal. With low output, the burner starts automatically after cleaning. If the fault occurs repeatedly, the setting of the CO2 valves need checking
2950 B	No flame signal. Following starting the procedure the burner starts automatically. After cleaning set the correct gas/air ratio correctly
2963 B	The signal from the flow and heat exchanger temperature sensor is outside the permissible range – the connecting lead needs to connect correctly
2964 B	The flow rate in the heat exchanger is too low
2965 B	The flow temperature is too high
2966 B	Flow temperature rise in heat exchanger is too rapid
2967 B	Flow/heat exchanger temperature sensor differential is too great
2970 B	Pressure drop in the heating system is too rapid
2971 B	System pressure is too low – the heating system needs venting or water needs topping up until the preset pressure is reached. Replace the cable to the pressure sensor replace the pressure sensor

Worcester 4000 error codes

Brand new Worcester 4000 error codes, thee are easily read on their new LCD colour screen.

Fault Code	Description
1021	Cylinder charging or hot water temperature sensor faulty.  Turn the appliance off and back on again. The hot water sensor has been changed if an open or short circuit or refitted to the pipe if it has fallen off.
224	Software issue. Arrange a visit from a Worcester Bosch engineer to reset the boiler/PCB.

Greenstar CDi Highflow error codes

Fault Code	Description
A1	Pump is dry or running with air in the system – check system pressure
A5	Tank negative thermistor coefficient (NTC) defect
A7	Domestic hot water (DHW) negative thermistor coefficient (NTC) defect
A8	Energy Management System (EMS) communication error
B1	Code plug not detected
B2, B3, B4, B5, B6	Data error
B7	Burner control error
C6	Fan defect
D3	External temperature limiter
D5	Condensate pump failure
D6	Internal heat bank overflow
EA	Flame not detected – contact a Gas Safe engineer
E2	Primary negative thermistor coefficient (NTC) defect
E9	Safety temperature limiter in central heating (CH) flow stat tripped
F0	Internal error
F1	ROM fault
F7	Flame detected after the appliance has been shut off
FA	Flame detected after gas shut off
FD	Reset button pressed – try pressing the reset button again

Greenstar CDi Compact error codes

Fault Code	Description
T1	Ignition test – checking the igniter spark
T2	Fan test – checking the basic fan
T3	Pump test – checking the basic pump
T4	Three-way valve test
T6	Ionisation oscillator test
9A 362	Error – incorrect HCM fitted
9U 233	Heat Control Module (HCM) error – problem with code plug
B7 257	Internal error – possible control board problem
C6 215	Fan problem – fan is running too fast
C7 214	Fan problem – fan is not running
D1 240	Return sensor error – sensor may be wet or damaged
E2 222	Flow sensor short circuit error
E5 218	Flow temperature is too high
E9 219	Safety sensor fault – temperature is too high, sensor short circuit or open circuit
EA 227	No flame detected or flame signal loss during operation-contact a Gas Safe engineer – Possible blockage (frozen condensate pipe)
F0 237	Internal error
F7 228	Flame error – false flame or flame detected before burner started
FA 306	False flame fault – flame detected after the burner has stopped
FD 231	Mains power fault – electrical power interruption
FA 364	Gas valve EV2 leak test failed – gas valve leak
FB 365	Gas valve EV1 leak test failed
A1 281	Pump stuck or running with air in the system
C1 264	Airflow stopped during the operation
C4 273	Airflow present during last 24 hours
D1 240	Return sensor short circuit
D4 271	The temperature difference between flow and safety sensor exceeds the limit
E9 224	Max thermostat activated – flue gas thermostat overheat
EA 227	No ionisation is detected after ignition (Check frozen condensate pipe)
EF 349	Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212	Safety or flow temperature is rising too fast

Greenstar CDi Classic Regular error codes

Fault Code	Description
B1	Code plug not detected
C6	Fan speed too low
E2	Central heating (CH) flow negative thermistor coefficient (NTC) sensor defective
E9	Safety temperature limiter in central heating (CH) flow has tripped
EA	Flame not detected -contact a Gas Safe engineer
F0	Internal error
F7	Flame detected even though appliance is switched off
FA	Flame detected after gas shut off
FD	The reset button pressed by mistake

Greenstar CDi Fi Regular error codes

Fault code	Description
b1	Code plug is not detected
C6	Fan speed is too low
E9	Safety temperature limiter in CH flow has tripped
EA	Flame not detected – contact a Gas Safe engineer
F0	Internal error
F7	Flame detected even though the boiler is switched off
FA	Flame detected after gas shut off
FD	The reset button pressed by mistake

Greenstar i System 27/30 error codes

Fault Code	Description
T1	Ignition test – checking the igniter spark
T2	Fan test – checking the basic fan
T3	Pump test – checking the basic pump
T4	Three-way valve test
T6	Ionisation oscillator test
9A 362	Error – incorrect HCM fitted
9U 233	Heat Control Module (HCM) error – problem with code plug
B7 257	Internal error – possible control board problem
C6 215	Fan problem – fan running too fast
C7 214	Fan problem – fan not running
D1 240	Return sensor error – sensor may be wet or damaged
E2 222	Flow sensor short circuit error
E5 218	Flow temperature too high
E9 219	Safety sensor fault – temperature too high, sensor short circuit or open circuit
EA 227	No flame detected or flame signal loss during operation (check frozen condensate pipe)
F0 237	Internal error
F7 228	Flame error – false flame or flame detected before burner started
FA 306	False flame fault – flame detected after the burner stopped
FD 231	Mains power fault – electrical power interruption
FA 364	Gas valve EV2 leak test failed – gas valve leak
FB 365	Gas valve EV1 leak test failed
A1 281	Pump stuck or running with air in the system
C1 264	Airflow stopped during the operation
C4 273	Airflow present during last 24 hours
D1 240	Return sensor short circuit
D4 271	The temperature difference between flow and safety sensor exceeds the limit
E9 224	Max thermostat activated – flue gas thermostat overheat
EA 227	No ionisation detected after ignition ( Check frozen condensate pipe)
EF 349	Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
NO CODE 212	Safety or flow temperature rising too fast

Greenstar i Combi and System 9/24 boiler error codes

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

Greenstar Heatslave 11 error codes

Fault Code	Description
E9210	Maximum temperature thermostat or air pressure switch activated. Reset overheat thermostat or air pressure switch before resetting the boiler
E5218	Flow temperature too high
E9219, 220 or 221	Safety temperature too high, safety sensor short circuit or safety sensor open circuit
E2222, 223 or 233	Flow sensor short circuit, flow sensor open circuit, or heat control module code plug missing or defective
F0237 or 238	Software relay error – Resistors between plus X4 pins 3 & 5 disconnected or water in the burner control box
F0239 or 259	Watchdog relay error or A/D reference relay error – If the error persists, change the control board
F0263	Appliance powered off with locking fault present – press reset button to clear
D4271	The temperature difference between flow and safety sensors exceeds the limit
E9276 or 277	Flow temperature or safety temperature exceeds 95°C
F0278, 279 or 290	Sensor test error, A/D convertor error, or A/D convertor reference error
E5332	Primary flow has exceeded 105°C – primary sensor overheated
9A360	Incorrect HCM for boiler variant – replace with correct HCM
A7808	DHW sensor defective – check and replace defect sensor as necessary
A0809	Thermal store sensor defective – check and replace defect sensor as necessary
9F855 or 856	Burner 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.
H29	Warning triangle and house symbol displayed on the controller – weather compensation activated but no weather sensor detected.
H27	Warning 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 Code	Description
No light	No power at the control board
Light on	Appliance 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 flash	Volatile lockout sensor fan or code plug
2 pulses	Check service mode switch is in minimum position
5 pulses	Check service mode switch is in max position

GB162 error codes

Fault code	Description
208	The boiler is currently in chimney sweep mode.
200	The boiler is in heating mode.
201	The boiler is in domestic hot water (DHW) mode.
202	The boiler is waiting – there was a heat demand from the on-off or modulating control.
203	The boiler is on standby.
204	The boiler is waiting – the actual temperature is higher than the calculated or selected boiler temperature.
212	The temperature recorded by the flow temperature sensor or the safety sensor is rising too quickly.
260	The flow temperature sensor is not detecting a rise in temperature following a burner start.
265	The boiler is waiting in response to a heat demand – the boiler regularly switches to partial load.
268	The boiler is in a component test phase.
270	The boiler is modulating upwards.
283	The boiler is preparing for a burner start – the fan and pump are activated.
284	The gas valve has switched.
305	The 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 317	There is a short circuit in the flue gas temperature sensor contacts.
C6 216	The fan speed is too low.
CE 207	The water pressure is too low.
CE 266	The pump test failed.
D1 241	The contacts of the boiler return temperature sensor have been interrupted.
D3 232	The external switching contact has opened.
D4 213	The actual temperature recorded by the flow temperature sensor or return temperature sensor is rising too quickly.
D4 286	The boiler return temperature sensor has detected a return temperature higher than 105°c.
E2 223	The flow temperature sensor contacts have been interrupted.
E9 210	The temperature measured by the flue gas sensor is too high and is open.
E9 220	The contacts for the safety temperature sensor have shorted or the safety temperature sensor has detected a temperature higher than 130°c.
E9 277	The safety temperature sensor has measured temperature in excess of 95°c.
E9 285	The boiler return temperature sensor has measured a temperature higher than 95°c.
E9 318	The flue gas temperature sensor contacts have been interrupted.
EA 234	The contacts of the gas valve have been interrupted.
EA 269	The ignition device has been activated for too long.
GB162	The ignition device has been activated for too long.
F0 278	The sensor test has failed – cabling and plug sensors need checking.
F0 279	The burner control unit, or KIM, is faulty – the control unit may need replacing.
F0 287	The burner control unit, or KIM, has an error.
F7 328	A brief power failure has occurred.
EC 256	The burner control unit has an error.
H07	The current water pressure is too low, limiting the performance in heat mode as well as domestic hot water (DHW) mode.
rE	The boiler resets.