What to check, in order
- Check the condensate pipe outside
Worcester says a frozen or blocked condensate pipe shuts the boiler down. In freezing weather, look along the outside section.
- Thaw it gently
Hold a hot water bottle, a microwaveable heat pack or a cloth soaked in hot water against the frozen part. Don't use boiling water, and only do this if the pipe is at ground level and easy to reach.
- Reset and wait
Hold the reset button for 5 seconds, then wait two to three minutes for the boiler to restart.
When to call a Gas Safe engineer
If d5 stays after the pipe is clear, call a Gas Safe registered engineer to look at the condensate pump.
Good to know
- This meaning is from Worcester's manual for the Greenstar FS CDi. A code can mean something different on another range, so check the manual for your model.
Parts people end up buying
Only if the checks above point to a part. Match it to your model number first: it's on a label on the data badge, usually under the boiler or behind the front cover.
- Condensate pipe insulationSearch on Amazon
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Quick answers
What does the Worcester Bosch D5 fault code mean?
On Worcester's Greenstar FS CDi floor-standing boilers, d5 means a fault with the condensate pump, which pumps the boiler's waste water away.
Can I fix Worcester Bosch D5 myself?
Easy (about 20 minutes). Start with: check the condensate pipe outside; thaw it gently; reset and wait. If d5 stays after the pipe is clear, call a Gas Safe registered engineer to look at the condensate pump.
Is Worcester Bosch D5 worth repairing?
Worth fixing. If the pipe was frozen, it costs nothing. If not, the condensate pump is a part an engineer can replace.
Checked against
- Worcester Bosch Greenstar FS CDi user instructions (PDF)
- Worcester Bosch Greenstar CDi Classic user instructions (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.