Common problems guide

The most common Worcester Bosch Greenstar 15sbi problems

The faults most likely to send a Worcester Bosch Greenstar 15sbi into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
3 documented codes
3 most common
1 DIY-safe checks
2 engineer needed

The 3 most common faults

01
LOCKOUT LIGHT FLASHING High DIY-safe

Your boiler has stopped working because it failed to light or stay lit, which has triggered a safety shutdown.

Why it happens: This fault occurs when the boiler tries to light the burner but fails to detect a stable flame after several attempts. The most common reasons are a lack of gas reaching the unit, worn-out spark components that can no longer create a flame, or a sensor that is too dirty to 'see' the flame once it has started.

What to try first

Check if your gas supply is active and credit is on your meterPress the reset button once to see if the boiler restartsEnsure any external gas valves are in the open position

Est. cost
£120-350
Parts
Spark electrode, Flame sense electrode, Gas valve
Full guide for LOCKOUT LIGHT FLASHING
02
lock-out High Engineer

Your boiler has failed to ignite after several attempts and has switched itself off for safety reasons, meaning it cannot currently provide heat or hot water.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for lock-out
03
LOCKOUT LIGHT ON (CONSTANTLY) High Engineer

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

Est. cost
£120-250
Parts
Overheat thermostat, Central heating pump, NTC sensor
Full guide for LOCKOUT LIGHT ON (CONSTANTLY)
Parts most often replaced

on the Worcester Bosch Greenstar 15sbi

Spark electrodeFlame sense electrodeGas valveIgnition leadIgnition electrodePCB

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Worcester Bosch shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 3-code list for the Worcester Bosch Greenstar 15sbi

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →