BoilerFaultCodesThe 6 most common faults
01
Low Water Pressure High DIY-safe
Your boiler has detected that there is not enough water in the system to operate safely, which is usually caused by a small leak or air being bled from radiators.
What to try first
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the one or two taps/valves until you hear water flowing.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps tightly.
02
PCB Fault High Engineer
Your boiler's main electronic control board has not been properly set up or programmed for your specific boiler model.
Full guide for PCB Fault03
Lockout 6 High Engineer
Your boiler is temporarily shutting down because its sensor thinks a flame is present inside when it shouldn't be.
Full guide for Lockout 604
Boiler Type Card Fault High Engineer
Your boiler's control system is unable to read or recognise its internal setup card, meaning it cannot operate safely.
Full guide for Boiler Type Card Fault05
PCB Replacement High Engineer
Your boiler has detected an issue with its internal memory chip or main control board, meaning it cannot operate safely and has shut down.
Full guide for PCB Replacement06
Overheat Lockout High Engineer
Your boiler has temporarily shut itself down because the internal water temperature got too high.
Full guide for Overheat Lockouton the Keston Combi 30
Filling loopPressure sensorExpansion vesselPrinted Circuit Board (PCB)Flame detector electrodeBoiler Control Card
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