Common problems guide

The most common Worcester Bosch Greenstar 30 CDi System problems

The faults most likely to send a Worcester Bosch Greenstar 30 CDi System 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.
11 documented codes
6 most common
0 DIY-safe checks
6 engineer needed

The 6 most common faults

01
A7 Engineer

Hot water NTC sensor defective. Check hot water NTC sensor and connecting lead for circuit breaks/short circuits.

Full guide for A7
03
b1 Engineer

Code plug not detected. Insert code plug correctly, test and replace if necessary.

Full guide for b1
04
C6 Engineer

Fan speed too low. Check fan lead and connector, and fan; replace as necessary.

Full guide for C6
06
E9 Engineer

Safety temp. limiter in CH flow has tripped. Check system pressure, check safety temp. limiters, check pump operation, check fuse on pcb, bleed appliance.

Full guide for E9

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 11-code list for the Worcester Bosch Greenstar 30 CDi System

Related guides

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