BoilerFaultCodesWorcester Bosch 1-C6 Fault Code
Also written as 1C6 — same fault.
The Worcester Bosch 1-C6 fault code means: your boiler has detected that the water pressure in the system is outside of the normal operating range, which often means it needs topping up or has been overfilled.. It appears on 1 Worcester Bosch model in our database.
Technical description: System pressure: Current system pressure
What causes the Worcester Bosch 1-C6 fault?
This fault occurs when the internal sensor detects that the system pressure has dropped below 0.6 bar or risen above a safe maximum. The most common reason is a slow loss of water through the radiators or a leak, but it can also happen if the filling link was left open after topping the boiler up. When the pressure leaves this safe zone, the boiler's safety software restricts operation to prevent internal damage.
This fault is more common in autumn when homeowners first turn their heating back on after summer, as air can get trapped or seals may have shrunk during the period of inactivity.
DIY fix possible
Locate the internal or external filling link (often a blue lever or braided hose under the boiler).Slowly open the valve(s) until the pressure gauge on the display shows between 1.0 and 1.5 bar.Ensure both valves are closed tightly once the correct pressure is reached.
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Gas Safe Register →Worcester Bosch models that show the 1-C6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-C6 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