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Worcester Fault Codes

Complete reference guide for all Worcester Bosch boiler fault codes. Find your error code below for detailed causes and step-by-step solutions. Worcester Bosch boilers include Greenstar, CDi, GB162, and all other ranges.

Listed below are all Worcester Bosch fault codes as described by the boiler manufacturer along with possible causes. Click “View Solution” for detailed step-by-step fixes, DIY tips, and when to call a Gas Safe engineer.

Worcester Bosch boilers display fault codes in different formats depending on model and age:
– Modern boilers show alphanumeric codes (EA, C6, A1, etc.)
– Some models use number codes with suffixes (227 V, 1017 W, etc.)
– Older CDI Highflow models use LED flash patterns
– Greenstar Ri models use LED light sequences

Find your boiler model below and locate your fault code.

David C Osborne Heating

Worcester Bosch Common Fault Codes (Most Models)

Fault CodeDescriptionPossible CauseSolution
EA / EA 227 / EA 229No flame detected or flame lossGas supply, electrode, or frozen condensate pipeView Solution →
E9 / E9 219Safety temperature limiter trippedOverheat – low pressure or circulation faultView Solution →
CE / CE 207Water pressure too lowSystem pressure below minimumView Solution →
D5Low water pressure (some models)System pressure too lowView Solution →
C6 / C6 215/216Fan speed issueFan running too fast or too slowView Solution →
C7 / C7 214/217Fan not runningFan stopped or won’t startView Solution →
E2 / E2 222/223Flow sensor faultTemperature sensor shorted or disconnectedView Solution →

 

Worcester Bosch CDI Classic Combi

Fault CodeDescriptionPossible CauseSolution
A1Water leak or pump issuePump running dry or needs replacingView Solution →
A7Hot water NTC sensor defectiveSensor or connecting leads faultView Solution →
A8Communication break to sensorElectrical connections need checkingView Solution →
B1Code plug not detectedCode plug missing or faultyView Solution →
C6Fan speed too lowFan lead and connector issueView Solution →
E2CH flow NTC sensor defectiveFlow sensor or connection faultView Solution →
E9Safety temperature limiter trippedSystem pressure or limiter faultView Solution →
EAFlame not detectedGas supply, igniter, or electrode issueView Solution →
F0Internal errorElectrical connector or interface faultView Solution →
F7Flame detected when switched offElectrode wet or PCB/flue issueView Solution →
FAFlame detected after gas shut offGas valve needs checkingView Solution →
FDReset button pressed by mistakePress reset againView Solution →

Worcester Bosch CDi Compact / Greenstar 25/30 Si / 27/30 I

Fault CodeDescriptionPossible CauseSolution
T1Ignition testSystem testing igniter sparkNo action – test mode
T2Fan testSystem testing fanNo action – test mode
T3Pump testSystem testing pumpNo action – test mode
T4Three-way valve testSystem testing valveNo action – test mode
T6Ionisation oscillator testSystem testing ionisationNo action – test mode
9A 362Incorrect HCM fittedWrong Heat Control ModuleView Solution →
9U 233HCM errorProblem with code plugView Solution →
B7 257Internal errorPossible control board problemView Solution →
C6 215Fan running too fastFan problemView Solution →
C7 214Fan not runningFan faultView Solution →
D1 240Return sensor errorSensor wet or damagedView Solution →
E2 222Flow sensor short circuitSensor shortedView Solution →
E5 218Flow temperature too highOverheat conditionView Solution →
E9 219Safety sensor faultTemperature too high or sensor faultView Solution →
EA 227No flame detectedIgnition failureView Solution →
F0 237Internal errorControl issueView Solution →
F7 228False flame errorFlame before burner startedView Solution →
FA 306False flame faultFlame after burner stopView Solution →
FD 231Mains power faultElectrical power interruptionView Solution →
FA 364Gas valve EV2 leak test failedGas valve leakView Solution →
FB 365Gas valve EV1 leak test failedGas valve leakView Solution →
A1 281Pump stuck or air in systemPump running with airView Solution →
C1 264Airflow stopped during operationFan/airflow issueView Solution →
C4 273Airflow present during last 24 hoursContinuous operationView Solution →
D4 271Temperature difference exceeds limitFlow/safety sensor differenceView Solution →
E9 224Max thermostat activatedFlue gas thermostat overheatView Solution →
EF 349CH boil detectedOperating at minimum load issueView Solution →
NO CODE 212Safety/flow temperature rising too fastRapid temperature riseView Solution →

Worcester Bosch Greenstar I System / Combi

Fault CodeDescriptionPossible CauseSolution
226Service tool connectedBlocking error history menuView Solution →
FD 231Power interrupted during lockoutPower failureView Solution →
C7 214Fan doesn’t run during start-upFan harness connector issueView Solution →
C6 215Fan speed too highFan harness problemView Solution →
C7 216Fan speed too lowFan harness problemView Solution →
C7 217Fan stopped during operationFan failureView Solution →
C1 264Fan stopped during operationFan issueView Solution →
C4 273Continuous fan for 24 hoursAppliance temporarily blockedView Solution →
E2 222Flow temperature sensor shortedSensor faultView Solution →
E2 233Flow temperature sensor disconnectedSensor unpluggedView Solution →
E9 276Primary flow exceeded 95°COverheatView Solution →
FA 306Ionisation after gas valve closedFlame detection issueView Solution →
EA 227No ionisation after ignitionIgnition failureView Solution →
F7 228Ionisation before burner startFalse flameView Solution →
EA 229Loss of ionisation during operationFlame lossView Solution →
EA 261HCM potentially defectiveReset applianceView Solution →
9U 233Control box or HCM defective/looseCheck HCMView Solution →
C4 237Control box or HCM defectiveControl faultView Solution →
F0 238Gas valve or control box errorGas valve coils need checkingView Solution →
F0 239-290Control box or HCM defectiveVarious control faultsView Solution →
328Internal error with mains voltageFrequency inconsistentView Solution →
235Incompatible HCM softwareControl box needs updateView Solution →
356Low mains voltageVoltage interrupted/inconsistentView Solution →
360HCM invalidIncorrect HCM for control boxView Solution →
A8 362Low mains voltage or invalid HCMVoltage or HCM issueView Solution →
CC 800Outdoor sensor defectExternal sensor faultView Solution →
A1 281Pump stuck or running dryPump issueView Solution →
E9 224Flue/high limit thermostat activatedOverheat lockoutView Solution →
D4 341Primary flow temperature rising too fastRapid temperature riseView Solution →

Worcester Bosch GB162

Fault CodeDescriptionPossible CauseSolution
200Boiler in heating modeNormal operation statusNo action – normal
201Boiler in DHW modeNormal operation statusNo action – normal
202Boiler waitingHeat demand presentNo action – normal
203Boiler on standbyNo heat demandNo action – normal
204Boiler waitingTemperature higher than setNo action – normal
208Chimney sweep modeService mode activeNo action – test mode
212Temperature rising too quicklyFlow/safety sensor rising fastView Solution →
226Diagnosis tool connectedNow locked outView Solution →
235KIM too new for burner controlSoftware incompatibilityView Solution →
260No temperature rise after burner startSensor not detecting riseView Solution →
265Boiler waiting – regular switch to partial loadNormal modulationNo action – normal
268Component test phaseTesting modeNo action – test mode
270Boiler modulating upwardsNormal operationNo action – normal
283Preparing for burner startFan/pump activatedNo action – normal
284Gas valve switchedNormal operationNo action – normal
305Waiting for DHW to endNormal operationNo action – normal
360KIM not compatibleIncompatible moduleView Solution →
9A 361Burner control not compatibleIncompatible control unitView Solution →
9U 233Burner control or KIM faultyModule faultView Solution →
A3 317Short circuit in flue gas sensorSensor faultView Solution →
B7 257Burner control or KIM faultyControl faultView Solution →
C1 264No control signal to fanFan power issueView Solution →
C4 273Boiler off – operated 24+ hoursAutomatic shutdownNo action – normal
C6 215Fan speed too highFan faultView Solution →
C6 216Fan speed too lowFan faultView Solution →
C7 214Fan doesn’t run during startFan faultView Solution →
C7 217Fan speed irregular at startFan issueView Solution →
CE 207Water pressure too lowLow system pressureView Solution →
CE 266Pump test failedPump faultView Solution →
D1 240Return sensor short circuitSensor shortedView Solution →
D1 241Return sensor interruptedSensor disconnectedView Solution →
D3 232External switching contact openedExternal control issueView Solution →
D4 213Temperature rising too quicklyRapid temp riseView Solution →
D4 271Temperature differential too highFlow/safety sensor differenceView Solution →
D4 286Return temperature > 105°CSevere overheatView Solution →
E2 222Flow sensor short circuitSensor shortedView Solution →
E2 223Flow sensor interruptedSensor disconnectedView Solution →
E5 218Flow temperature > 105°CSevere overheatView Solution →
E9 210Flue gas sensor too high/openSensor faultView Solution →
E9 219Safety sensor > 105°COverheatView Solution →
E9 220Safety sensor shorted or > 130°CSevere overheatView Solution →
E9 224Safety sensor interruptedSensor disconnectedView Solution →
E9 276Flow sensor > 95°COverheatView Solution →
E9 277Safety sensor > 95°COverheatView Solution →
E9 285Return sensor > 95°COverheatView Solution →
E9 318Flue gas sensor interruptedSensor disconnectedView Solution →
EA 227Insufficient ionisation after ignitionIgnition failureView Solution →
EA 229Insufficient ionisation during operationFlame lossView Solution →
EA 234Gas valve contacts interruptedGas valve faultView Solution →
EA 261Burner control unit faultyControl faultView Solution →
EA 269Ignition device activated too longIgnition issueView Solution →
F0 238-290Burner control unit or KIM faultyVarious control faultsView Solution →
F7 228Ionisation before burner startFalse flameView Solution →
F7 328Brief power failure occurredPower interruptionView Solution →
FA 306Ionisation after burner outFalse flame after shutdownView Solution →
FD 231Mains interrupted during faultPower lossView Solution →
EC 256Burner control unit errorControl faultView Solution →
EH 258Burner control unit faultyCheck wiringView Solution →
H07Water pressure too lowLimited performanceView Solution →
HrEBoiler keeps resettingRepeated reset attemptsView Solution →
rEBoiler resetsReset occurringNo action if clears

Worcester Bosch CDI Highflow LED Flash Codes

Note: Older CDI Highflow models use LED flash patterns instead of display codes:

LED PatternDescriptionSolution
Light offNo boiler demandNo action – normal
Light onHeating demand – boiler OKNo action – normal
1 flash, 5 sec offNo ionisation after ignitionView Solution →
2 flashes, 5 sec offLoss of ionisation during operationView Solution →
3 flashes, 5 sec offGas valve errorView Solution →
4 flashes, 5 sec offSafety timing error / ignition timingView Solution →
5 flashes, 5 sec offMultiple faults (see below)View Solution →
4 flashes, gap, 1 longSensor test failedView Solution →
4 flashes, gap, 2 longSafety temperature too highView Solution →
4 flashes, gap, 3 longMax safety thermostat activatedView Solution →
4 flashes, gap, 4 longReturn temperature too highView Solution →
4 flashes, gap, 5 longFlow temperature > 110°CView Solution →
1 long, 4 quick (repeated)HCM defectiveView Solution →
2 long, 4 quick (repeated)Fan issues (too fast/slow/not running)View Solution →
3 long, 4 quick (repeated)Mains voltage interrupted after lockView Solution →
4 long, 4 quick (repeated)Internal control board faultsView Solution →
5 long, 4 quick (repeated)Miscellaneous faults – reset boilerView Solution →

5 flashes can indicate:

  • Ionisation detected after burner stopped
  • Gas valve EV2 leak test failed
  • Gas valve EV1 leak test failed
  • Ionisation current before burner start
  • Gas valve error
  • Ionisation sensor shorted

Worcester Bosch Greenstar Ri LED Codes

LED PatternDescriptionSolution
No lightNo power at control boardCheck power supply
Light onAppliance on but not operatingNo action – standby
Slow flash (mostly off)Ignition lockoutView Solution →
Slow flash (mostly on)Flue/heat exchanger overheatView Solution →
Fast flashVolatile lockout – sensor/fan/code plugView Solution →
2 pulsesService mode switch in minimum positionCheck switch
5 pulsesService mode switch in max positionCheck switch

Worcester Bosch Greenstar 8000 Status & Fault Codes

CodeTypeDescriptionSolution
200 OStatusBoiler in heating modeNo action – normal
201 OStatusBoiler in hot water modeNo action – normal
202 OStatusBoiler in anti-cycle modeNo action – normal
203 OStatusStandby – no heat demandNo action – normal
204 OStatusCurrent temp higher than setNo action – normal
208 OStatusChimney sweep demandTest mode
224 VFaultSafety limiter trippedView Solution →
227 VFaultNo flame signal after ignitionView Solution →
228 VFaultFlame signal without flameView Solution →
305 OStatusHot water anti-cycle modeNo action – normal
306 VFaultFlame after closing fuel supplyView Solution →
360 VFaultIncompatible code plugView Solution →
815 W/BFaultLow loss header temp sensor faultyView Solution →
1010 OFaultNo BUS communicationView Solution →
1017 WFaultWater pressure too lowView Solution →
1021 BFaultHot water temp sensor defectiveView Solution →
1022 BFaultHot water storage sensor defectiveView Solution →
1037 WFaultOutside temp sensor defectiveView Solution →
1065 BFaultPressure sensor defectiveView Solution →
1068 WFaultOutside temp sensor defectiveView Solution →
1073 WFaultShort circuit of flow temp sensorView Solution →
1074 WFaultNo signal from flow temp sensorView Solution →
1075 WFaultShort circuit at heating block sensorView Solution →
1076 WFaultNo signal from heating block sensorView Solution →
2920 VFaultError with flame monitoringView Solution →
2924 VFaultNo feedback from modulating gas valveView Solution →
2925 VFaultGas valve feedback too lowView Solution →
2927 BFaultFlame failed during operationView Solution →
2946 VFaultIncorrect code plug detectedView Solution →
2948 BFaultNo flame signalView Solution →
2950 BFaultNo flame signal after startView Solution →
2963 BFaultFlow/heat exchanger sensor out of rangeView Solution →
2964 BFaultFlow rate in heat exchanger too lowView Solution →
2965 BFaultFlow temperature too highView Solution →
2966 BFaultFlow temperature rise too rapidView Solution →
2967 BFaultFlow/heat exchanger differential too greatView Solution →
2970 BFaultPressure drop too rapidView Solution →
2971 BFaultSystem pressure too lowView Solution →

Code Suffixes:

  • O = Operating status (normal)
  • V = Volatile fault (locks out)
  • W = Warning
  • B = Blocking error (requires reset)

Most Common Glow-worm Faults

CE / D5 - Low Pressure

The most common Worcester fault. Easy DIY fix - repressurise your heating system to 1.0-1.5 bar using the filling loop.

EA 229 - Flame Loss

Very common in winter. Usually caused by frozen condensate pipe blocking drainage. Can often be fixed by thawing the pipe.

E9 - Overheat Lockout

Safety limiter has tripped due to overheat. Usually low pressure, pump fault, or circulation issue. Check pressure first.

⚠️ Winter Warning: EA 229 & D5 Frozen Condensate Pipe

If your Worcester Bosch boiler is showing EA 229 or D5 during cold weather, your condensate pipe is almost certainly frozen. This is the #1 cause of Worcester boiler breakdowns in winter.

**Quick Fix You Can Do:**
1. Locate the condensate pipe outside – white or grey plastic, 21-32mm diameter
2. Pour warm (NOT boiling) water slowly along the full length of the pipe
3. You’ll hear gurgling sounds when the blockage clears
4. Reset your boiler by turning the mode selector to reset position
5. The boiler should fire up normally

**Why This Happens:**
The condensate pipe carries acidic water from your boiler to a drain. In freezing conditions, this water freezes solid, blocking the pipe and preventing the boiler from operating safely.

**Permanent Prevention:**
Have a Gas Safe engineer install proper pipe insulation or reroute the pipe internally. This costs £50-150 and prevents all future freezing issues – much cheaper than repeated emergency callouts!

**Still showing EA 229 after thawing?** Call us: 01304 381999

When To Call An Engineer

❌ NEVER Attempt DIY:

  • Ignition faults (EA, EA 227, EA 229) – after trying condensate
  • Gas valve faults (FA, FA 306, FA 364, FB 365, 3 flashes)
  • Fan faults (C6, C7, 2 long/4 quick flashes)
  • PCB faults (F0, B7 257, EH 258, 4 long/4 quick flashes)
  • Sensor faults (E2, D1, A7, A3 317, 1073-1076)
  • Overheat faults (E9, E5) – after checking pressure
  • Control module issues (9U 233, 9A 361/362, 360)
  • Pump faults (A1, CE 266)
  • HCM errors (Heat Control Module)
  • False flame issues (F7, F7 228)
  • Any gas-related fault
  • Any fault involving electronics
  • Any fault you’re unsure about

These require Gas Safe registered engineers with Worcester Bosch Accredited Installer status and diagnostic equipment.

✅ You CAN Try:

  • Low pressure (CE, D5, CE 207, H07, 1017 W, 224 V, 2971 B) – Repressurise to 1.0-1.5 bar
  • Thaw frozen condensate pipe (EA 229, D5 in winter)
  • Reset boiler after power cut (FD, FD 231)
  • Check power supply (no light on Ri models)
  • Ensure gas supply is on
  • Check isolation valves are open
  • Bleed radiators if system has air
  • Turn mode selector to reset position

How to Repressurise Worcester Bosch:
1. Turn boiler to OFF
2. Locate filling loop (usually under boiler – internal or external)
3. **Internal key type:** Turn key anticlockwise
4. **External loop type:** Open both small valves
5. Watch pressure gauge reach 1.0-1.5 bar (green zone)
6. Close valves/turn key back
7. Turn boiler back to heating mode

Important: If EA 229 returns after thawing, or CE returns within days, call an engineer. Repeated faults indicate underlying problems that won’t be fixed by resetting.

Need Help With Your Worcester Bosch Boiler?

Our Gas Safe registered engineers are Worcester Bosch Accredited Installers serving Kent and surrounding areas. We stock genuine Worcester parts for same-day repairs.

✓ Same-day emergency callouts available
✓ All major brands serviced and repaired

📞 Call 01304 381999
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Worcester Quick Fixes Before Calling

**External Filling Loop (Common):**
1. Turn boiler to OFF
2. Find the silver braided hose with 2 small black valves (usually under boiler)
3. Turn BOTH valves anticlockwise slowly
4. Watch the pressure gauge – stop at 1.0-1.5 bar (green zone)
5. Turn both valves clockwise to close
6. Turn boiler back to heating mode

**Internal Filling Key Type:**
1. Turn boiler to OFF
2. Locate the filling key (often stored in a pocket under the boiler)
3. Insert key into keyhole and turn anticlockwise
4. Watch pressure gauge reach 1.0-1.5 bar
5. Turn key clockwise and remove
6. Store key safely
7. Turn boiler back to heating

**Never exceed 1.5 bar** – over-pressurisation can damage seals and cause leaks.

**Standard Reset:**
Turn the mode selector knob fully anticlockwise to the reset position (flame with cross symbol), wait 2 seconds, then turn back to heating or auto.

**Alternative Method (if above doesn’t work):**
1. Turn mode selector to OFF (or 0)
2. Wait 30 seconds
3. Turn back to heating position
4. Boiler should restart

**After EA 229 (frozen condensate):**
Always reset after thawing the pipe. If fault returns immediately, the pipe may still be frozen or there’s another issue.

**Important:** Don’t repeatedly reset without fixing the underlying problem. Three failed resets mean you need an engineer.

Your fault code format depends on your Worcester model:

**If you see:** EA, E9, C6, FD, A1 = CDI Classic, CDi Compact, or Greenstar I

**If you see:** Numbers with V/W/B/O (like 227 V, 1017 W) = Greenstar 8000 or GB162

**If you see:** Flashing LED lights (no display) = CDI Highflow or Greenstar Ri

**If you see:** T1, T2, T3, etc = Boiler in test mode (normal during servicing)

**Not sure?** Check the rating plate inside the boiler casing or look at your manual.

**Locating Your Condensate Pipe:**
– Usually 21-32mm white or grey plastic pipe
– Runs from bottom of boiler to outside drain
– Often visible on exterior wall near boiler
– May exit through wall near boiler position
– Can be traced from boiler’s condensate outlet

**Thawing Instructions:**
1. Use warm (NOT boiling) water – boiling can crack the pipe
2. Pour slowly along entire visible length
3. Focus on the lowest point where water collects
4. Listen for gurgling – this means it’s clearing
5. May need 2-3 kettles of water
6. Reset boiler once gurgling stops

**Prevention:**
Proper insulation costs £50-150 and prevents future freezing. Much cheaper than winter emergency callouts at £150-250!

Worcester FAQs

EA 229 means loss of ionisation signal during burner operation – essentially flame loss. In winter, this is almost always caused by a frozen condensate pipe blocking the boiler’s drainage system. In other seasons, it could indicate: gas supply interruption, electrode fault, or flue blockage. Try thawing the condensate pipe first (pour warm water along it), then reset once. If EA 229 returns, call a Gas Safe engineer immediately.

CE means low water pressure (or CE 207 on some models). Your system pressure has dropped below the minimum safe level, usually below 0.7 bar. To fix: Turn off the boiler, locate the filling loop (silver braided hose under boiler or internal key), open the valves slowly until pressure reaches 1.0-1.5 bar on the gauge, close the valves, turn boiler back on. If pressure drops again within days, you have a leak and need an engineer to locate and repair it.

Both are flame-related faults but occur at different times: EA 227 means no ionisation was detected after the ignition sequence – the boiler tried to light but couldn’t detect a flame. EA 229 means the flame was lit successfully but then lost during operation. EA 227 is usually gas supply or electrode issues. EA 229 in winter is typically frozen condensate pipe. Both require the same troubleshooting: check gas supply, try thawing condensate pipe, reset once. If persistent, call an engineer.

E9 means the safety temperature limiter has tripped due to overheating. This is a safety lockout to prevent damage. Common causes: low system pressure, pump failure, blocked system, closed radiator valves, or airlock. What to try: 1) Check pressure (should be 1.0-1.5 bar), 2) Ensure all radiator valves are open, 3) Bleed radiators if they have air, 4) Reset boiler once. If E9 returns or pressure is OK, you likely have a pump or circulation problem – call a Gas Safe engineer. Don’t ignore E9 as repeated overheating can damage the heat exchanger.

Turn the mode selector knob (usually on the front panel) fully anticlockwise to the reset position – marked with a flame symbol with a line through it. Hold for 2 seconds, then turn back to the heating or auto position. The boiler will attempt to restart. On older models without a clear reset position, turn to OFF (or 0), wait 30 seconds, then turn back to heating. Important: If the same fault returns immediately, there’s an underlying problem – don’t keep resetting, as this can damage components. Call an engineer after 2-3 failed resets.

D5 is an alternative code for low water pressure on some Worcester models (same as CE on others). The system pressure is too low for safe operation. Fix by repressurising the system to 1.0-1.5 bar using the filling loop. If you see D5 during cold weather, it could also indicate a frozen condensate pipe – try thawing the pipe before repressurising. If D5 returns frequently, you have a leak in the system that needs professional repair.

Worcester Bosch recommends annual servicing by a Gas Safe registered engineer, preferably a Worcester Accredited Installer. Annual servicing: maintains your warranty (essential for warranty claims), prevents expensive breakdowns, optimizes efficiency (saves money on gas bills), ensures safe operation, provides landlord gas safety certificates. Worcester boilers have excellent reliability, but annual servicing catches small issues before they become expensive failures. We offer annual service plans with automatic reminders for all Worcester models.

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