Question 1

Worcester Boiler Fault Codes

Accepted Answer

Common DIY-Fixable Codes
A1 281 / No Code 212 / 1017 W: Low water pressure. Check your pressure gauge; if it is below 1 bar, you likely need to top up the system using the filling loop.
EA 227 / EA 229: No flame detected. This can be caused by a frozen condensate pipe during winter. Try thawing the external pipe with warm (not boiling) water or a hairdryer.
SE: Not a fault. This indicates the boiler has reached a service interval and is due for its annual maintenance.

Common Worcester Bosch Fault Codes
LOW PRESSURE / WATER FLOW
A1 – Low system pressure (water needs topping up)
212 – Water pressure too low
1017 W – System pressure below 0.5 bar
281 – Pump stuck or air in the system
E2 222 – Flow sensor short circuit or defect
FLAME & GAS ISSUES
EA 227 – No flame detected (gas supply issue or ignition failure)
EA 229 – Loss of flame signal during operation
D1 240 – Return sensor fault
FA 306 – Flame detected after gas valve has closed
FA 364 – Gas valve or burner error
OVERHEATING & SENSORS
E9 219 – Safety sensor has detected temperature over 105°C
E9 224 – Flue thermostat or high-limit thermostat tripped
A7 – Hot water temperature sensor fault
A8 209 – Communication error between the boiler and controls
FAN & VENTILATION
C6 215 – Fan speed too high
C7 214 – Fan speed too low or fan stopped
D3 232 – External safety limiter (overheat) triggered
ELECTRICAL & INTERNAL
F0 290 – Internal electronic error (PCB failure)
B1 – Code plug error
EF – Boiler is in "siphon cleaning" mode (not a fault, wait 15 minutes)
MAINTENANCE
SE – Service due (the boiler requires its annual service)

Question 2

Main Heating Boiler Fault Codes

Accepted Answer

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Main Heating Boiler Fault Codes
E1 / E110 (Overheating)
Issue: System temperature is too high or safety thermostat has tripped.
Action: Check for a jammed pump or air in the circuit. Turn the selector switch to 'Reset' for 5 seconds. If it persists, call an engineer. 
E118 / E119 (Low Water Pressure)
Issue: System pressure is below 0.5 bar.
Action: Repressurise the system via the filling loop until the gauge reads approximately 1.5 bar. 
E125 (Circulation Fault)
Issue: Primary water is not circulating correctly.
Action: Check the pump and for any closed valves or airlocks. 
E133 / E128 (Ignition/Flame Failure)
Issue: Interrupted gas supply or flame not detected.
Action: Check if the gas meter is on and reset the boiler. In winter, this can indicate a frozen condensate pipe. Thaw external pipes if necessary. 
E160 (Fan Fault)
Issue: The fan is not running or there is a wiring error.
Action: Requires an engineer to inspect the fan and connection. 
E168 (System Error)
Issue: The boiler has detected a general electrical or PCB problem it cannot identify.
Action: Reset the boiler. If the code returns, a Gas Safe engineer is required. 
Sensor Faults (E20, E28, E50)
E20: Central Heating NTC sensor error.
E28: Flue NTC sensor error.
E50: Domestic Hot Water NTC sensor error.
Action: Professional engineer required to test or replace sensors.

Question 3

Vokera Boiler Fault Codes

Accepted Answer

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Common Vokèra Boiler Fault Codes
LOW PRESSURE / WATER ISSUES
04 / A04 – Insufficient water pressure (system needs topping up)
AL40 / AL41 – Low system pressure
E040 / E041 – Water transducer fault / check system water pressure
E042 – Water transducer defect
40 / 41 – Low pressure detected (specific models) 
IGNITION & GAS FAILURES
01 / A01 – Ignition failure (boiler cannot detect a flame)
10 / A10 – Ignition or flame detection issue
E10 – Flame lockout
A11 / E011 – False/extraneous flame detected
F09 – Ignition failure 
OVERHEATING & SENSORS
02 / A02 – Overheat fault / limit thermostat trip
06 / A06 – Domestic hot water (DHW) thermistor fault
07 / A07 – Primary flow thermistor fault (water too hot or sensor defect)
08 / A08 – Return thermistor fault
F10 – Overheat thermostat tripped
E020 – Limit thermostat fault 
FAN & FLUE ISSUES
03 / A03 – Fan fault (mechanical failure or obstruction)
E030 – Fan malfunction
A09 / E090 – Flue gases over-temperature or flue thermistor fault
92 / 93 / 95 – Condensate pipe blockage (often frozen in winter) 
INTERNAL & ELECTRICAL
05 – Communication fault
F01 – Fan or fan speed sensor fault
E058 – Main voltage error
E065 – Current modulation alarm
ADJ – Calibration mode active 
SERVICE & STATUS
_CL – Call for service (boiler is due for maintenance)
ACO – Service operation in progress
_St – Autostop (safety shutdown)
P (Blinking) – Preheating function active

Question 4

Poterton Boiler Fault Codes

Accepted Answer

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Common Potterton Boiler Fault Codes
WATER PRESSURE & CIRCULATION 
E119 / E1 / E118 – Low system water pressure (below 0.5 bar; needs topping up)
E117 – System pressure too high (above 2.9 bar)
E125 – Primary water circulation fault (pump failure or airlock)
E109 – Poor circulation / Pre-circulation fault
E193 – General circulation issue 
IGNITION & FLAME ISSUES
E133 – Ignition failure (could be gas supply, frozen condensate pipe, or ignition lead)
E128 – Loss of flame during operation
E129 – Loss of flame during calibration
E384 – False flame detected (flame detected when gas valve is off)
E135 – Internal error / Interruption of gas supply 
OVERHEATING & THERMISTORS
E110 – Boiler overheat (safety thermostat tripped)
E20 / E120 – Central heating thermistor (NTC) sensor fault
E50 / E321 – Domestic hot water (DHW) sensor fault
E28 – Flue thermistor fault
E130 / E131 – Flue thermostat sensor tripped / Flue overheat lockout 
FAN & MECHANICAL
E160 / E161 – Fan fault (loose connections, damaged fan, or PCB communication issue)
E53 – Flue obstruction
E09 – Gas valve wiring fault
E15 – Gas valve connection/command fault 
ELECTRICAL & COMMUNICATION
E168 – PCB lockout (internal electronic error; often requires a reset or engineer visit)
E151 / E152 / E167 – Printed Circuit Board (PCB) error
E83 / E84 / E85 / E86 / E87 – Communication error between room controller and boiler
E385 – Low voltage (less than 195v)

Question 5

Vaillant Boiler Fault Codes

Accepted Answer

Common Vaillant Fault Codes
WATER PRESSURE & CIRCULATION
F.22 – Low water pressure (system needs topping up)
F.23 – Temperature spread too great (pump blockage or circulation issue)
F.24 – Temperature rising too quickly (pump failure or air in system)
F.75 – Pump or pressure sensor fault (no pressure change detected when pump starts)
F.83 – Temperature rise too slow (insufficient water or sensor fault) 
IGNITION & FLAME ISSUES
F.27 – False flame detected (incorrect flame signal)
F.28 – Ignition failure (failed to light after multiple attempts)
F.29 – Flame extinguished during operation (gas supply or flue issue)
F.54 – Gas supply fault (often appears with F.28/F.29) 
OVERHEATING & SENSORS
F.20 – Overheating lockout (safety thermostat triggered)
F.00 / F.01 – Flow or return temperature sensor defect (interrupted or loose)
F.10 / F.11 – Flow or return sensor short circuit
F.25 – Flue gas temperature too high
F.76 – Overheat protection on the primary heat exchanger 
FAN & ELECTRICAL
F.32 – Fan fault (defective fan or wiring problem)
F.49 – eBUS fault (low voltage or short circuit in controls)
F.61 – Gas valve regulation fault (electronic control or gas valve error)
F.62 – Gas valve switch-off delay (valve leaking or PCB fault)
F.63 – EEPROM error (main PCB failure)
F.65 – Electronics temperature too high
Con / Connection – Communication error between PCB and display

DIY Troubleshooting Tip: If you see F.22, you can often fix this yourself by repressurising your boiler to between 1.0 and 1.5 bar. For most other codes, especially those involving gas (F.28, F.29) or internal electronics (F.61, F.63), you must contact a GAS SAFE

Question 6

Glow-Worm Boiler Fault Codes

Accepted Answer

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Glow-worm Boiler Fault Codes
F22 / F9 (Low Water Pressure)
Issue: System pressure has dropped too low (usually below 0.5 bar).
Action: Repressurise the system using the filling loop until the gauge is between 1.0 and 1.5 bar. This is the most common Glow-worm fault.
F1 / F4 / F28 / F29 (Ignition or Flame Failure)
Issue: The boiler cannot light or has lost its flame.
Winter Tip: Often caused by a frozen condensate pipe. Thaw external pipes with warm (not boiling) water. If not frozen, check the gas supply and reset.
F3 (Fan or Air Pressure Fault)
Issue: The fan is not reaching the correct speed to safely exhaust gases.
Action: An engineer is required to inspect the fan, wiring, or air pressure switch.
F5 / F20 (Overheating)
Issue: The boiler has reached an unsafe temperature and shut down.
Action: Check that radiator valves are open and the pump is running. Allow to cool and try a reset. If it recurs, call an engineer.
F11 / F13 / F61-F67 (PCB / Electrical Fault)
Issue: Communication error between internal circuit boards or a main board failure.
Action: Requires professional diagnostic. These codes usually indicate a component failure or wiring issue.
F75 (Pressure Sensor / Pump Fault)
Issue: The boiler doesn't detect a pressure increase when the pump starts.
Action: Often indicates a failed pump or a blocked pressure sensor. Requires a Gas Safe engineer.
Technical Sensors (F00, F01, F10, F71)
Issue: Errors with flow or return temperature sensors (NTC).
Action: Professional engineer required to test sensors or wiring harnesses.

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