BoilerFaultCodesWorcester Bosch 1-C2 Fault Code
Also written as 1C2 — same fault.
The Worcester Bosch 1-C2 fault code means: your boiler's internal pump is running at an incorrect speed, which could lead to your heating or hot water not working effectively.. It appears on 1 Worcester Bosch model in our database.
Technical description: Pump modulation: Actual heating pump modulation.
What causes the Worcester Bosch 1-C2 fault?
This fault occurs when the boiler's control system detects that the internal pump is spinning at a different speed than required. The most common reasons are a buildup of debris or 'sludge' inside the pump that physically slows it down, or a communication failure between the pump and the main circuit board.
This issue often surfaces in autumn when the heating is turned back on after summer, as internal components can seize or become sluggish during long periods of inactivity.
DIY fix possible
Turn the boiler off at the fused spur switch for 30 seconds and turn it back on to reset the electronics.Check that all radiator valves are fully open to ensure water can flow freely.Listen for any unusual grinding or humming noises coming from the boiler casing.
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-C2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-C2 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