BoilerFaultCodesWorcester Bosch E01-840 Fault Code
Also written as E01840 — same fault.
The Worcester Bosch E01-840 fault code means: your boiler has lost water pressure, and the internal component used to refill it is likely disconnected or faulty.. It appears on 1 Worcester Bosch model in our database.
Technical description: Charging Link Assembly
What causes the Worcester Bosch E01-840 fault?
This fault occurs when the boiler detects that the system water pressure has dropped too low to operate safely. The specific error indicates that the internal mechanism used to refill the system is either physically disconnected, incorrectly inserted, or the sensor monitoring the water flow into the unit has failed. Essentially, the boiler cannot verify that it is being topped up with water, so it shuts down to prevent damage.
This issue often appears after the first cold spell of autumn when homeowners turn their heating back on and discover the system has naturally lost pressure over the summer months.
DIY fix possible
Locate the internal filling link (white key or lever) at the bottom of the boilerEnsure the key is pushed in fully and turned to the locked positionTurn the grey square knob to top up the pressure until the needle is between 1 and 1.5 bar
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Gas Safe Register →Worcester Bosch models that show the E01-840 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch E01-840 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