BoilerFaultCodesWorcester Bosch 1.C Fault Code
Also written as 1C — same fault.
The Worcester Bosch 1.C fault code means: your boiler is struggling to pump water around your home correctly because it cannot find the right speed setting for your heating system.. It appears on 1 Worcester Bosch model in our database.
Technical description: Pump map (heating - combi & system only)
What causes the Worcester Bosch 1.C fault?
This fault occurs when the boiler's control board loses communication with the internal pump or cannot determine the correct flow rate for your radiators. It is usually caused by a mechanical failure within the pump itself or a glitch in the main circuit board that prevents it from sending the correct speed signals. In some cases, a build-up of debris in the system can also put too much strain on the pump, causing it to fail this internal check.
This issue often comes to light in autumn when the heating is turned on for the first time after summer, as the pump can seize up during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the 1.C fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1.C 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