BoilerFaultCodesThe 6 most common faults
Your boiler has encountered a critical system error and has shut itself down as a safety precaution.
Why it happens: This fault occurs when the boiler's internal computer experiences a major communication failure or a critical hardware error. It typically happens because the main control board can no longer safely monitor the unit's operation, leading to an immediate shutdown to prevent damage. The most common trigger is a sudden electrical surge or a terminal failure of the electronic components inside the boiler.
Full guide for EnnYour boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the external filling loop, usually two silver valves connected by a braided metal hose underneath the boiler.Gradually open the valves to let mains water into the system until the pressure gauge on the front reads between 1.0 and 1.5 bar.Close both valves firmly and check for any visible leaks around your radiators or pipework.
Your boiler has lost power entirely, which could be due to a simple tripped switch or an internal electrical failure.
Check if other appliances in the house have powerCheck your home's main fuse box for a tripped circuit breakerEnsure the boiler's isolation switch (switched spur) is turned on
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the external filling loop, which is usually a flexible silver braided hose connecting two pipes near the boiler.Open the valves at both ends of the hose to allow water into the system while watching the pressure gauge on the front of the boiler.Stop filling when the needle reaches the green zone (typically between 1.0 and 1.5 bar) and ensure both valves are tightly closed.
Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.
Full guide for E 02Your boiler has detected that the power was turned off and back on again while it was already trying to deal with a fault, causing the system to lock itself for safety.
Full guide for E 04on the Keston C55
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Keston shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue