BoilerFaultCodesYour boiler has lost water pressure, and the internal component used to refill it is likely disconnected or faulty.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Charging Link Assembly
What causes this 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
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E01-840 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Worcester Bosch 24/28CDi II RSF is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.