D5
Worcester Bosch Boiler
Severity:What Does This Error Mean?
D5 means the condensate pump has failed or the condensate pipe is blocked. The boiler will not run safely until the fault is resolved. Check for a frozen or blocked condensate pipe first.
Affected Models
- Worcester Bosch Greenstar 8000
- Worcester Bosch Greenstar 4000
- Worcester Bosch Greenstar CDi
- Worcester Bosch Greenstar i System
Common Causes
- Condensate pump motor seized or failed
- Condensate pipe frozen in cold weather
- Condensate trap full and overflowing
- Float switch in the pump stuck in fault position
How to Fix It
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Check the condensate pipe for blockage or freezing.
If the condensate pipe runs outside (common in many installations), it can freeze in winter. Thaw the pipe by applying warm — not boiling — water externally along its length.
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Listen for the condensate pump activating.
When the boiler fires, you should briefly hear the condensate pump running. Silence means the pump has likely seized. A running pump that still shows D5 points to a blocked outlet pipe or stuck float switch.
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Check the condensate trap.
Some Worcester Bosch models have a condensate trap that requires periodic emptying. Consult your installation manual for its location and the emptying procedure.
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Reset the boiler after clearing the fault.
Press the reset button on the boiler control panel. D5 clears if the condensate system is now functioning correctly.
When to Call a Professional
D5 condensate pump faults usually require a Gas Safe registered engineer to inspect and replace the pump or clear internal blockages.
Frequently Asked Questions
Can I run a Worcester Bosch boiler with D5 showing?
No. D5 is an active fault that prevents safe operation. Running with a failed condensate system can cause acidic condensate to overflow inside the boiler and damage components.
How often do condensate pumps fail on Worcester Bosch boilers?
Condensate pump lifespan is typically 5–10 years. Hard water, high usage, and acidic condensate from certain flue configurations can shorten pump life. Annual boiler service includes checking the condensate system.