BoilerFaultCodes.com

Worcester Bosch Highflow 400 BF Fault Codes

Combi Natural GasLPG 24 kW 1994-2003 Discontinued
GC Number: 47-311-30

Replaced by: Greenstar Highflow 440CDi

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Most common fault codes

6A
Your boiler is failing to light the gas or isn't staying lit, meaning you currently have no heating or hot water.
May be DIY safe · £120-350
6C
Your boiler thinks it sees a flame even though it hasn't turned the gas on, which is often caused by a faulty sensor or moisture in the system.
Gas Safe engineer required · £120-£350
6d
Your boiler is not receiving enough gas to operate correctly, which is preventing it from staying lit.
Gas Safe engineer required · £120-350

All 39 fault codes

Code Severity Plain English
6A High Your boiler is failing to light the gas or isn't staying lit, meaning you currently have no heating or hot water.
6C High Your boiler thinks it sees a flame even though it hasn't turned the gas on, which is often caused by a faulty sensor or moisture in the system.
6d High Your boiler is not receiving enough gas to operate correctly, which is preventing it from staying lit.
9U High Your boiler has stopped working because the internal fan is not spinning fast enough to safely clear waste gases from the system.
A1 Medium Your boiler has detected that a internal pump protective cover is loose or has moved out of its correct position.
A3 Emergency Your boiler has detected that the external cover is not sealed correctly, which is a safety feature designed to prevent combustion gases from escaping.
A4 Medium Your boiler's hot water sensor is struggling to communicate with the main control board, meaning the system cannot accurately monitor the temperature of your hot water.
A7 High Your boiler has detected an internal communication error with its memory chip, which is preventing the system from running correctly.
b1 High Your boiler's internal computer chip is missing or not making a proper connection, which means the system doesn't know which settings to use and has stopped working.
C1 Medium Your boiler has a buildup of mineral deposits that is preventing the water from heating up correctly and may cause it to make a loud kettle-like noise.
C4 High Your boiler has detected that a safety sensor is stuck, preventing it from starting its ignition sequence for heating or hot water.
C6 High Your boiler has stopped working because the internal fan, which safely exhausts gases, is either not spinning or not being detected by the system.
CC Low Your boiler has lost connection with its outdoor temperature sensor, which helps it adjust the heating based on the weather outside.
E2 High Your boiler's internal computer chip is no longer being recognised or has malfunctioned, meaning the unit cannot safely control its heating functions.
E5 High Your boiler has detected that a safety link or an external underfloor heating thermostat is missing or disconnected, causing the system to stop running for protection.
E9 High Your boiler has overheated, causing it to shut down automatically to protect its internal components and your home's safety.
EA High Your boiler has tried to light several times but cannot detect a flame, causing the system to lock out for safety.
F0 High Your boiler has detected a problem with the internal sensor that measures the temperature of the water used to heat your radiators.
F7 Emergency Your boiler thinks a flame is still burning inside the unit even though it has been told to turn off.
FA Emergency Your boiler is sensing a flame even though the gas should be turned off, which is a safety conflict that requires a professional inspection.
Fd High Your boiler is failing to light the flame properly even though gas is reaching the unit, meaning you will have no heating or hot water until a technician inspects the internal components.
H1 High Your boiler has encountered an internal electronics failure that is preventing it from starting up correctly.
H4 High Your boiler is sensing a flame even though it hasn't been asked to turn on, which is often caused by moisture or a sensor fault.
H8 High Your boiler is sensing a flame even though the gas should be turned off, leading the system to shut down as a safety precaution.
H9 Low Your boiler has paused because the reset button was pressed briefly and simply needs another press to confirm and restart.
overheat lock-out state High Your boiler has switched itself off because it has reached an internally high temperature and needs a manual restart to clear the safety lock.
POINT B High Your boiler's internal pump has stopped circulating water, which means your heating and hot water will not function.
POINT C High Your boiler has detected an internal safety shutdown because the fan that clears exhaust gases is not running.
POINT D High Your boiler is failing to ignite the burner at the required power, meaning it cannot provide heating or hot water.
POINT E High A small cooling fan inside the boiler's control panel has stopped working, which prevents the system from starting to ensure the electronics do not overheat.
POINT F Medium Your boiler's internal pump is failing to run its normal cooling-down cycle after you turn the heating off, which could cause the unit to overheat.
POINT G High Your boiler has switched itself off because the internal fan that clears exhaust gases has stopped working.
POINT H High Your boiler is failing to circulate water when you turn on a hot tap, meaning you will likely have no hot water.
POINT I High Your boiler is struggling to switch between providing heating and hot water, meaning you likely have no hot water available.
POINT J High Your boiler is receiving a request to turn on the heating, but it is failing to respond or light up correctly.
POINT K High Your boiler is failing to circulate water for your radiators, meaning your heating will not warm up despite being turned on.
POINT L High Your boiler is failing to light the burner correctly, meaning it cannot heat your home or water.
POINT M High Your boiler's flame is failing to stay lit or start properly when it needs to run at its lowest power setting.
POINT N High Your boiler is failing to switch between providing hot water and heating, meaning your central heating may not turn on even when the system is calling for it.

Status & diagnostic codes

These codes indicate your boiler's operating state or a diagnostic reading — not necessarily a fault. Status codes (S.) mean normal operation; diagnostic codes (D.) are informational readings used by engineers.

Code Type Description
d1 Diagnostic Your boiler has detected that a internal sensor responsible for monitoring water temperature returning to the unit is faulty or disconnected.

Worcester Bosch Highflow 400 BF is discontinued — time for a new one?

Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.

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