Common problems guide

The most common Worcester Bosch Greenstar CDi Classic (2012) problems

The faults most likely to send a Worcester Bosch Greenstar CDi Classic (2012) 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.

The 6 most common faults

01

A1 High Engineer

Your boiler has detected that the internal water pump is not working properly, which usually happens because it is stuck or has run without water.

Est. cost: £150-350
Parts: Central heating pump, Pump automatic air vent, Printed circuit board (PCB)

Full guide for A1

02

A8 High Engineer

Your boiler has lost its connection to its external thermostat or control unit, meaning it cannot properly receive instructions to turn the heating on.

Est. cost: £90-180
Parts: Room thermostat, Wiring centre, Main control board

Full guide for A8

03

b1 High Engineer

Your boiler has temporarily lost communication with an internal electronic identification chip, meaning it cannot safely start up.

Est. cost: £100-250
Parts: Code Plug, Printed Circuit Board (PCB)

Full guide for b1

04

C6 High Engineer

Your boiler has detected that the internal fan responsible for safely pushing out exhaust gases is not spinning fast enough.

Est. cost: £150-300
Parts: Flue assembly, Fan, Printed Circuit Board (PCB)

Full guide for C6

05

E2 High Engineer

Your boiler has temporarily stopped working because it cannot accurately read the temperature of the water flowing through your heating system.

Est. cost: £120-£220
Parts: CH flow NTC thermistor, Wiring harness

Full guide for E2

06

E9 High Engineer

Your boiler has temporarily shut down because the internal water temperature reached an unsafe limit.

Est. cost: £150-300
Parts: High limit thermostat, Circulation pump, PCB

Full guide for E9

Parts most often replaced

on the Worcester Bosch Greenstar CDi Classic (2012)

Central heating pumpPump automatic air ventPrinted circuit board (PCB)Room thermostatWiring centreMain control board

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 12-code list for the Worcester Bosch Greenstar CDi Classic (2012)