BoilerFaultCodesWorcester Bosch 1.d Fault Code
Also written as 1D — same fault.
The Worcester Bosch 1.d fault code means: your boiler has detected that the internal pump is not rotating at the correct speed to circulate water through your heating system.. It appears on 1 Worcester Bosch model in our database.
Technical description: Map pump step (heating - combi & system only)
What causes the Worcester Bosch 1.d fault?
This fault occurs when the boiler's control board expects the internal pump to be spinning at a specific speed but detects that it is struggling or stationary. The most common reasons are a build-up of sludge debris seizing the pump's internal components or an electrical failure in the pump's motor or wiring. Without the pump moving water away from the heat exchanger, the boiler shuts down to prevent internal overheating.
This issue often surfaces at the start of autumn when the heating is turned back on after being idle all summer, allowing debris to settle and seize the pump.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the 1.d fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1.d fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026