BoilerFaultCodesThe 4 most common faults
01
RED LOCKOUT BUTTON High DIY-safe
Your boiler has detected a safety or performance problem and has shut itself down to prevent damage.
What to try first
Check that your gas supply is active and credit is on the meterEnsure the condensate drain pipe outside has not frozen in cold weatherPress and hold the red reset button for three seconds to restart the system
02
CONDITION 1 High Engineer
Your boiler has detected a fault and has safely shut itself down to prevent damage, leaving you without heating and hot water.
Full guide for CONDITION 103
CONDITION 2 High Engineer
Your boiler is trying to start its ignition sequence, but it is stuck at the stage where the fan is running and it cannot confirm if the flame has successfully lit.
Full guide for CONDITION 204
CONDITION 3 High Engineer
Your boiler is trying to start up but the burner refuses to ignite, meaning it cannot produce any heat for your home or water.
Full guide for CONDITION 3on the Keston R-sm 20 FB
Ignition ElectrodeGas ValvePCBThermistorPrinted Circuit Board (PCB)Flame Sensing Probe
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