Worcester Bosch Greenstar 12Ri Fault codes & diagnostics

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

Regular Natural GasLPG 12 kW 2004-2018 Discontinued
GC Numbers 41-406-4141-406-4241-406-4341-406-4441-406-4541-406-4641-406-4741-406-4841-311-64

Replaced by: Greenstar 12Ri Compact

Download the Worcester Bosch Greenstar 12Ri 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 →

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
41-406-41 Greenstar 12Ri ErP 2015–2018
41-406-42 Greenstar 12Ri ErP LPG 2015–2018
41-406-43 Greenstar 15Ri ErP 2015–2018
41-406-44 Greenstar 15Ri ErP LPG 2015–2018
41-406-45 Greenstar 18Ri ErP 2015–2018
41-406-46 Greenstar 18Ri ErP LPG 2015–2018
41-406-47 Greenstar 24Ri ErP 2015–2018
41-406-48 Greenstar 24Ri ErP LPG 2015–2018
41-311-64 Greenstar 12 Ri 2004–2015
Just want the most common Worcester Bosch Greenstar 12Ri faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 4 documented codes

Tap any card for details

LED / flash-pattern codes
Fast flash

Your boiler has detected a critical internal fault and has locked itself out to prevent damage or unsafe operation.

High Engineer only £120-350

Parts commonly replaced

  • Temperature Sensor (NTC Thermistor)
  • Fan Assembly
  • Code Plug
  • Wiring Harness
Full explanation for Fast flash
Slow flash (unspecified rate)

Your boiler has detected that it cannot safely get rid of exhaust gases, so it has stopped working to prevent a buildup of dangerous fumes.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue pressure switch
  • Venturi
  • Fan assembly
  • Flue seals
Full explanation for Slow flash (unspecified rate)
Digital codes
flame lock-out

Your boiler is trying to start but the flame isn't catching, so it has safely shut itself down to prevent gas from building up.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
Full explanation for flame lock-out
No light

Your boiler appears to have no power and the display is completely dead, meaning it cannot provide any heating or hot water.

High DIY-safe £120-350

What to check first

  1. Check if the main electricity switch for the boiler is turned on
  2. Check your home's consumer unit (fuse box) to see if a circuit breaker has tripped
  3. Replace the fuse in the external boiler spur switch with a new 3-amp fuse

Parts commonly replaced

  • Internal Fuse (F1)
  • Transformer
  • PCB (Main Control Board)
Full explanation for No light
Status & diagnostic codes

3 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

2 pulses Diagnostic Your boiler has been left in a manual testing mode after a service or inspection and needs to be switched back to its normal operating setting. 5 pulses Diagnostic Your boiler has been left in its internal testing mode, which is usually only used by engineers during a service or setup. Light ON Status Your boiler is switched on and ready to work, but it isn't responding when you turn up the heating or hot water, usually because an external controller or a valve is failing to tell the boiler to start.