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Worcester Boiler Fault Codes and Errors

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Worcester Bosch is a leading boiler brand with massive acceptance ratings. However, like many things, the Worcester boiler is a victim of poor maintenance and time. The latter is inevitable; however, proper care can keep your Worcester Bosch in excellent condition, even lengthen its life span. In the unfortunate circumstance of malfunctioning, Worcester will initiate a lockout procedure.

The shutdown procedure prevents further damage from the initial problem. Fortunately, your Worcester boiler will also display error codes that will unravel the specific situation for your Gas Safe engineer to sort out. The manual that comes with the boiler has a list of all the error codes. But man is to err, so we have listed all the error codes you can infer if you lose it.

If you notice an error code displayed, try resetting your boiler; if it does not work, you are better of calling a qualified gas engineer. Tempering with the inner parts of your boiler could fester the problem.

What are Worcester Boiler fault codes?

Worcester boiler error codes are alphanumerical codes that pop up on display in the case of a problem. The codes generally identify specific faults and ways of fixing them and are particularly useful to the Gas Safe registered engineer. The error shows them how best to handle the situation.

The error codes are divided into; blocking errors, fault errors, locking errors, cause errors and maintenance codes. Worcester Bosch has an extended range of models, and the fault codes vary in different models.

Types of Worcester Bosch error codes

  • Blocking errors – When a blocking error occurs, the Worcester boiler goes into a shutdown procedure immediately. However, unlike other errors, no error codes will be displayed. Instead, pressing the spanner or the return button will reveal the cause of the blockage, and the boiler will start generally operating once the problem is solved.
  • Locking errors – In case of a locking error, the boiler will display the error code, cause code and flash a warning triangle. After fixing the boiler, you will need to press the reset button for three seconds to clear the error.
  • Fault errors – Fault errors indicate the fault group. They are alphanumeric codes that appear on your boiler.
  • Cause errors – These are three-digit numbers that usually flashes on the display panel during a locking error. They never display during a blocking mistake or normal operating status. You can access them in the info menu via the spanner or the return button.
  • Maintenance codes – The maintenance codes are easily distinguishable. They start with an ‘H’ followed by a number. Luckily, maintenance codes do not initiate a lockout, but they act as a warning and require a check-up from a qualified gas engineer.

How to reset a Worcester boiler

Resetting the boiler can clear a few error codes that will not require you to contact a qualified gas engineer. We advise you to always resort to resetting your boiler before getting a Safe Gas registered engineer unless the boiler is displaying an EA error code. If your boiler fails to operate, calling a qualified gas engineer is the best course.

There are two ways of resetting a Worcester Bosch boiler depending on its boiler. Other models will have a clear ‘reset’ button that you press down for three seconds, while others will have a light at the end of the temperature dial, which you turn down until you reach the ‘reset’ point and then hold it there for three seconds.

Worcester Bosch Greenstar heat slave II Oil boiler fault codes

Fault code/ Cause code Description Possible causes/ solutions
E9 210 The maximum temperature thermostat or air pressure switch is activated. The flue gas or tank thermostat has over-heat. Reset the overheated thermostat or air pressure switch, then reset your boiler.
212 The safety or flow temperature is too high. The cause of the high temperature is an airlock or reduced water content.
E5 218 The flow temperature is too high. The primary sensor is overheated. Reset after 30 minutes.
E9 219,220 and 221 Safety temperature too high. The primary heat exchanger has overheated. Wait 30 minutes and rest.
E2 222, 223 The flow sensor has a short circuit The flow sensor open circuit or the plug for the heat control module code is missing or defective.
E2 233 Heat Control Module (HCM). HCM Code plug missing or defective.
F0 237, 238 Software relay error. Resistors between plus X4 pins 3 and 5 disconnected or water in the burner control box.
F0 239, 259  A/D reference relay error.  If the error persists, have a qualified engineer change the control board.
F0 263 Appliance powered off with locking fault present. Press the reset button to clear.
D4 271 The difference between flow and safety sensors temperature exceeds the limit.  Check the flow sensor is seated correctly on the flow pipe, and the primary heat exchanger should be at 15 degrees Celsius.
E9 276,277 Safety and flow temperatures exceed 95 degrees Celsius. Wait for the boiler to cool and reset after 30 minutes.
F0 278,279 and 290 There is a sensor test error, A/D convertor error or A/D convertor reference error.  If the error persists, have a qualified engineer change the control board.
E5 332 Primary flow has exceeded 105 degrees Celsius.  The primary sensor is overheated.
359 DHW outlet or storage tank exceeds 90 degrees Celsius. The pump and burner are blocked till the temperature falls below 90 degrees Celsius. Wait 30 minutes for temperatures to drop.
9A 360 Incorrect HCM for boiler variant.  Replace with correct HCM.
380 The inlet DCW temperature is higher than the DHW outlet temperature. Wait for 30 minutes before resetting.
A7 808 DHW sensor is defective.  Check and replace the defect sensor as necessary.
A0 809 Thermal store sensor defective check and replace defect sensor as necessary
9F 855,856 Burner lockout or five-burner lockouts resets intermittently. Ensure the burner and the oil supply is free of contaminants. After several lockouts, code 856 pops up on display.
H29 Warning triangle on the controller. It indicates the weather compensation is active, but no weather sensor detected.
H27 A warning triangle symbol on the controller. DCW in sensor defect.

Worcester Bosch Greenstar CDI Classic regular boiler error codes/ Greenstar CDI Fi Regular error codes.

Fault Code Possible cause/ How to fix it
B1 A code plug is not detected.
C6 Fan speed is too low. Check the fan harness and connector.
E2 Central heating (CH) flow and the (NTC) sensor are defective.
E9 The safety temperature limiter in CH flow has tripped.
EA The flame is not detected. Contact a qualified heating engineer.
F0 Internal error.
F7 Flame detected even though the appliance is off.
FA Flame detected after the gas is off.
FD Someone pressed the reset button by mistake.

Worcester Greenstar I Combi and system boiler error codes

Fault Code Possible cause/ How to fix it
226 There is a connection of the service tool to the blocking error history menu.
FD 231 Power interruption during a lockout.
C7 214 The fan fails to run during the start-up phase. The fan harness connector needs checking.
C6 215 Fan speed is too high. Contact a qualified heating engineer.
C7 216 Fan speed is too low. Have a registered engineer check your fan.
C7 217 The fan has stopped during appliance operation.
C1 264 The fan is not working during an operation.
C4 273 The fan has been running continuously for the last 24hours, and the appliance is temporarily blocked.
E2 222 Flow temperature sensor shorted.
E2 233 Flow temperature sensor disconnected.
E9 276 Primary flow temperature exceeded 95 degrees Celsius.
E2 350 Flow temperature sensor shorted.
E2 351 Flow temperature sensor disconnected.
FA 306 Ionisation takes place after the gas valve is closed.
EA 227 No ionisation after ignition.
F7 228 Ionisation current detected before burner start.
EA 229 No ionisation signal during operation.
EA 261 The heat control module (HCM) is potentially defective.
9U 233 The control is defective or loose, and the HCM needs attention.
C4 237 The control box is defective.
F0 238 Gas valve error or control box error. Check the gas valve coils.
F0 239 The control box is defective.  Check the control box connections.
F0 242 The control box is defective. Check the HCM and control box connections.
B7 257 The control box is defective. Check HCM or control box connections.
F0 258 The control box is defective. Check HCM or control box connections.
EH 258 The control box is defective. Check HCM or control box connections.
F1 259 The control box is defective. Check HCM or control box connections.

 

F0 262 The control box is defective. Check HCM or control box connections.
F1 263 The control box is defective. Check HCM or control box connections.
F0 272 The control box is defective.  Links need checking, or HCM is not inserted correctly and needs replacing.
F0 280 The control box is faulty. Connections need checking, or HCM is not inserted correctly and needs replacing.
F0 290 The control box is defective. Check HCM for incorrect insertion, or it may need replacing.
328 Internal error with the mains voltage.  The frequency may be inconsistent.
235 Incompatible software versions of HCM. The control box needs the latest software.
356 Low mains voltage. Check for inconsistent and interruptive voltage.
360 Heat control module (HCM) invalid. HCM does not correlate with the control box.
A8 362 Low mains voltage. Check for unstable and interruptive voltage.
CC 800 Outdoor sensor defect is available when the outdoor accessory 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.

Worcester CDI Classic Combi boiler Error codes

Fault Description Possible cause/ How to fix it
A1 The pump needs replacing or freeing as it is running dry or water is leaking.
A7 The NTC sensor is defective. Check the hot water sensor or connecting leads.
A8 Check the break communication to FX sensor controls electrical connections.
B1 A code plug is not connected.
C6 Fan speed is too low. The fan lead and connector may need replacing.
E2 Central heating (CH) water flows and NTC sensor are defective. Check the central heating flow, Negative thermistor coefficient (NTC) sensor.
E9 The safety temperature limiter in CH flow has tripped the system pressure. It needs checking by a heating engineer.
EA No flame observation. Check the gas supply, power supply or igniter, electrode and lead. Contact a heating engineer.
F0 Internal error. The electrical connector contacts or programmer interface module. Confirm the ignition leads are well fitted.
F7 Presence of flame even though the appliance is off. Ensure that the electrode assembly is dry and the flue is not clogged.
FA The presence of flame after turning the gas off. The gas valve needs checking. Contact a heating engineer.
FD The reset button was pressed by mistake. Press the reset button again.

Greenstar I system 27/30, Greenstar I system 25/30 and Greenstar CDI Compact error codes

Fault Code Possible cause/ How to fix it
T1 Ignition test. Check the igniter spark.
T2 Fan test. Check the basic fan
T3 Pump test. Check 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. Indicates an issue with the code plug.
B7 257 Internal error. Means a possible PCB problem.
C6 215 Fan problem. The fan is running too fast and should be checked by a qualified heating engineer.
C7 214 Fan problem. The fan is not running.
D1 240 Return sensor error. The sensors might be wet or damaged.
E2 222 Flow sensor short circuit error.
E5 218 Flow temperature too high.
E9 219 Safety sensor fault. The temperature is too high; the sensor has a short circuit or open circuit that needs checking.
EA 227 No flame or flame signal loss during operation.
F0 237 Internal error
F7 228 Flame error. False flame or flame observed before burner started.
FA 306 False flame fault. The flame was detected after the burner stopped.
FD 231 Mains power fault. This means there is an electrical power interruption.
FA 364 Gas valve EV2 leak test failed.  This means the gas valve is leaking.
FB 365 Failure of gas valve EV1 leak test
A1 281 The presence of air in the system or pump is stuck.
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 the flow and safety sensor surpasses the limitation.
E9 224 Activation of the max thermostat – flue gas thermostat overheat.
EA 227 No ionisation after ignition.
EF 349 Central heating boil detected

Boiler operating at the minimum burner load with temperature difference more significant than 18 degrees Celsius between Flow and Return.

NO CODE 212 Safety or flow temperature rising too fast.

Greenstar CDI Highflow error codes

Fault Code Possible cause/ How to fix it
A1 The pump is dry or running with air in the system. Check and adjust the pressure in the system.
A5 Tank negative thermistor coefficient (NTC) is defective
A7 Domestic hot water (DHW) or negative thermistor coefficient (NTC) is defective.
A8 Energy Management System (EMS) communication error
B1 The code plug is 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 is not detected. You should contact a Safe Gas registered engineer.
E2 The primary negative thermistor coefficient (NTC) is defective
E9 The safety temperature limiter in central heating flow is malfunctioning
F0 Detection of an internal fault.
F1 ROM error.
F7 Flame observed after the appliance is off.
FA Flame noticed after gas shut off
FD Reset button pressed. Try pressing the reset button again.

Greenstar 8000 error codes

Fault Code Possible cause/ How to fix it
200 O Boiler in heating mode
201 O Boiler in hot water mode
202 O Boiler in anti-cycle mode
203 O Boiler on standby.
204 O The current primary water temperature is above the set value.
208 O Chimney sweep demand
224 V The safety temperature limiter has tripped. Top up the water in your boiler until you reach the recommended pressure.
227 V No flame signal after ignition. Your burner control unit may need a replacement.
228 V Flame signal without a flame present. This is an indication that the air/gas ratio control valve or ionisation cable may need replacing
305 O Boiler in hot water anti-cycle mode
306 V Flame signal after shutting the fuel supply off. Another indication is that the air/gas ratio control valve may need replacing.
360 V Incompatible code plug. Check that the correct code plug is installed and exchange or reconnect the code plug.
815 W/B Low loss header temperature sensor faulty. Check the differential sensor or the sensor port for the wrong installation.
1010 O EMS-Bus is damaged or not connected, or there is no Bus communication. To fix it, replace the damaged cable exchange fuse or connect the cable for the EMS-Bus.

 

1017 W Water pressure too low. Check the boiler vent system and top up the water.
1021 B The hot water temperature sensor is defective. The sensor plug may not be connected or needs replacing.
1022 B The hot water storage temperature sensor is defective. Correctly connect the plug to the hot water temperature sensor or replace it.
1037 W The outside temperature sensor is defective. Check the connecting lead.
1065 B The pressure sensor is either defective or not connected. First, check the pressure sensor connection. If it needs replacing, contact a qualified heating engineer.
1068 W The outside temperature sensor is defective. Check the connecting lead.
1073 W Short circuit of the flow temperature sensor. Consider replacing the temperature sensor.
1074 W No signal from the flow temperature sensor detected or temperature sensor could need replacing.
1075 W The temperature sensor has a short circuit at the heating block
1076 W The temperature sensor gives no signal at the heating block is detected
2920 V Error with the flame monitoring
2924 V The modulating gas valve gives no feedback. The gas valve relay is defective. Press the reset button, then apply burner start. If the fault reoccurs, the gas valve may need replacements.
2925 V The feedback from the modulating gas valve is too low.
2927 B Flame failed during burner operation. Contact a qualified heating engineer.
2946 V Incorrect code plug detected. It may need replacing.
2948,2959 B No flame signal. The burner should turn on automatically after cleaning. Also, check the carbon dioxide setting.
2963 B The signal from the central heat flow and heat exchanger temperature sensor is outside the permissible range. Therefore, ensure the connecting leads are correctly connected.
2964 B The flow rate is too low in the heat exchanger. Contact a heating engineer.
2965 B The flow temperature is too high. Contact a heating engineer.
2966 B Flow temperature rise in heat exchanger is too rapid. Contact a heating engineer.
2967 B Central heat flow or temperature sensor differential is too great. Contact a heating engineer.
2970 B The pressure drop in the boiler system is too rapid. Repressurise the boiler.
2971 B System pressure is too low. The system needs venting or water topping to the desired pressure.

Greenstar Ri boiler error codes.

Fault Code Possible cause/ How to fix it
No light There is 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 overheats or heat exchanger overheat.
Fast flash Volatile lockout sensor fan or code plug.
Two pulses Check service mode switch is in minimum position.
Five pulses Check service mode switch is in max position. 

Is my Worcester Bosch boiler faulty?

The Worcester boiler models made within the last decade usually display errors on code control panels when they detect an internal issue. As such, any errors within the boiler are likely to be displayed. However, it is convenient to regularly check your boiler for signs of faults to counter the problem way before the damage happens.

And as always, don’t attempt to fix the boiler if you do not understand an error. Instead, contact a qualified heating engineer who will safely and effectively repair your boiler or advice you accordingly.

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