Worcester Bosch Greenstar 40 CDi Conventional Common Problems & Fault Codes (2026 Guide)

The most common Worcester Bosch Greenstar 40 CDi Conventional problems

The faults most likely to send a Worcester Bosch Greenstar 40 CDi Conventional 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 3 most common faults

F7 Engineer

Flame detected even though appliance switched off. Check electrode assembly, dry pcb. Flue clear?

Full guide for F7

FA Engineer

Flame detected after gas shut off. Check gas valve and wiring to gas valve. Clean condensation trap and check electrode assembly. Flue clear?

Full guide for FA

Fd Engineer

Reset button pressed by mistake. Press reset button again.

Full guide for Fd

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 40 CDi Conventional