Worcester Bosch 24CDi BF Fault codes & diagnostics

10 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural GasLPG 24 kW 1997-2005 Discontinued
GC Numbers 47-311-2947-311-3247-311-33

Replaced by: Greenstar 25i

Download the Worcester Bosch 24CDi BF manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 7 High 2 Medium
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-311-29 24 Cdi BF 1997–2005
47-311-32 24 Cdi OF 1997–2002
47-311-33 24 CDi - L OF 1997–2005
Just want the most common Worcester Bosch 24CDi BF faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 10 documented codes

Tap any card for details

LED / flash-pattern codes
CH light On (flashing)

Your boiler has temporarily stopped itself because it detected that the water inside is getting too hot, but it will attempt to restart automatically after a short cooling period.

Medium Engineer only £120-250

Parts commonly replaced

  • NTC Thermistor
  • Central Heating Pump
  • Plate-to-plate heat exchanger
Full explanation for CH light On (flashing)
Fast flash

Your boiler has detected a general internal fault and has locked itself out to prevent damage.

High DIY-safe £150-450

What to check first

  1. Turn the main power switch to the boiler off
  2. Wait for 30 seconds
  3. Turn the power back on to see if the fault clears

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Fan
  • Air Pressure Switch

Related codes

Full explanation for Fast flash
HW light On (flashing)

Your boiler has sensed that the water inside it is getting too hot and has automatically switched itself off to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • NTC thermistor
  • Primary heat exchanger
  • Pump
Full explanation for HW light On (flashing)
Slow flash

Your boiler has stopped running for safety reasons and needs to be manually restarted to try and get your heating and hot water back on.

High DIY-safe £100-300

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for at least one second.
  3. Wait for the boiler to restart; if the light stops flashing, the boiler should resume normal operation.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • PCB

Related codes

Full explanation for Slow flash
Digital codes
Air flow fault

Your boiler is struggling to clear air fumes properly, so it has safely shut down to prevent any unsafe conditions.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi
Full explanation for Air flow fault
Burner shut-down

Your boiler has temporarily turned itself off because it has become too hot to operate safely and needs to cool down before it can restart.

Medium Engineer only £150-300

Parts commonly replaced

  • Pump
  • Diverter valve
  • Primary heat exchanger
  • NTC sensor
Full explanation for Burner shut-down
Flue spillage device

Your boiler has detected that gases are not safely escaping through the flue and has shut itself down to protect your home from harmful fumes.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue thermostat
  • Flue terminal
  • Fan
Full explanation for Flue spillage device
Ignition lockout

Your boiler has failed to light the flame, so it has safely shut itself down to prevent any gas build-up.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for Ignition lockout
lockout

Your boiler is failing to light the flame, so it has purposefully shut down to prevent gas from escaping into your home.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • Gas valve
  • PCB
Full explanation for lockout
Overheat cut-off

Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • High limit thermostat
  • Central heating pump
  • Plate heat exchanger
  • Diverter valve
Full explanation for Overheat cut-off