Worcester Bosch Greenstar 15i System Fault codes & diagnostics

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

System Natural Gas 15 kW 2006-2012 Discontinued

Replaced by: Greenstar 15i System ErP

This boiler uses indicator light combinations

Note which lights are on, off, or flashing and at what speed. Match the combination to the cards below. Do not reset until you have noted the pattern. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 8 High
Just want the most common Worcester Bosch Greenstar 15i System faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 9 documented codes

Tap any card for details

LED / flash-pattern codes
Blue light: Off / Lockout: Off

Your boiler has completely lost all electrical power, meaning it cannot operate your heating or hot water at all.

High DIY-safe £100-250

What to check first

  1. Check your home's fuse box or consumer unit to see if the RCD or boiler circuit breaker has tripped.
  2. Verify the fused spur switch located near the boiler is turned on.
  3. Ensure the plug or connection at the fused spur is secure and the fuse inside the spur hasn't blown.

Parts commonly replaced

  • External fuse
  • Printed Circuit Board (PCB)
  • Transformer
Full explanation for Blue light: Off / Lockout: Off
Blue light: On / Lockout: Off

Your boiler is receiving a request for heating but cannot start the sequence, even though your hot water is still working perfectly.

High Engineer only £120-250

Parts commonly replaced

  • Diverter valve
  • External heating programmer
  • Room thermostat
  • PCB
Full explanation for Blue light: On / Lockout: Off
Digital codes
Burner does not ignite

Your boiler is failing to start because it is not receiving or burning gas as it should.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Ignition electrode
Full explanation for Burner does not ignite
Electrode does not spark

Your boiler is failing to ignite because it cannot create the spark needed to light the flame.

High Engineer only £150-250

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • Printed Circuit Board (PCB)
Full explanation for Electrode does not spark
Fan does not run

Your boiler has stopped working because it cannot properly move the air and fumes required for safe operation.

High Engineer only £150-300

Parts commonly replaced

  • Fan
  • Air pressure switch
  • Printed circuit board
Full explanation for Fan does not run
Flame does not persist

Your boiler safely shut itself off because it could not keep the flame lit to heat your water and radiators.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Burner seal
Full explanation for Flame does not persist
lock-out

Your boiler is failing to light the flame, so it has safely shut itself down to prevent a gas leak.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board
Full explanation for lock-out
LOCKOUT

Your boiler has stopped working because it cannot light its internal flame, which means your heating and hot water have switched off for safety.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
Full explanation for LOCKOUT
Pump does not run

Your boiler is failing to circulate water through your radiators or hot water tank, meaning your home will not be able to heat up.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for Pump does not run