Worcester Bosch D5 fault code — condensate pipe or pump issue
⚠️ This needs a qualified professional
This fault involves gas or mains electrical work. Don't attempt a DIY repair — UK law requires gas work to be carried out by a Gas Safe registered engineer. Below is what to check and describe to them, not step-by-step repair instructions.
A D5 fault on a Worcester Bosch boiler relates to condensate drainage — the boiler can’t get rid of the acidic water produced as a normal by-product of running. On models with a condensate pump (rather than a gravity-fed pipe), D5 usually points to the pump itself; on others it’s linked to the same frozen-pipe issue as the EA 229 code.
What’s safe to check yourself
- Find the white condensate pipe running from the boiler, usually to an outside drain — in cold weather, check for visible ice, especially where the pipe runs outside the house.
- If frozen and safely reachable, pour warm (not boiling) water over the icy section to clear it, then insulate the pipe with purpose-made pipe lagging to reduce the chance of it refreezing.
- If your system uses a separate condensate pump (more common on floor-standing boilers), you likely won’t be able to safely inspect this yourself — note it for the engineer instead.
When to call an engineer
If there’s no visible external ice, or the pipe is clear but D5 persists, the issue is inside the boiler’s drainage system or condensate pump — this needs a Gas Safe registered engineer, not further DIY attempts.