BoilerFaultCodesThe 6 most common faults
01
F2 High DIY-safe
Your boiler has lit correctly but the flame has gone out unexpectedly, causing the system to shut down for safety.
What to try first
Check if other gas appliances like your oven or hob are working to ensure gas is reaching the propertyCheck if your gas meter has credit (if using a pre-payment meter)Reset the boiler by pressing the reset button for five seconds
02
No power to boiler Engineer
Mains (Green) OFF, Boiler On (Yellow) OFF, Lockout (Red) OFF
Full guide for No power to boiler03
Boiler off on front Engineer
Mains (Green) Rapid Flash, Boiler On (Yellow) OFF, Lockout (Red) OFF
Full guide for Boiler off on front04
External controls not calling for heat Engineer
Mains (Green) Slow Flash, Boiler On (Yellow) OFF, Lockout (Red) OFF
Full guide for External controls not calling for heat05
Flow Overheat Engineer
Mains (Green) ON, Boiler On (Yellow) OFF, Lockout (Red) Flashing once every 2 seconds, DIAG LED 1 ON
Full guide for Flow Overheat06
Cabinet overheat Engineer
Mains (Green) ON, Boiler On (Yellow) OFF, Lockout (Red) Flashing once every 2 seconds, DIAG LED 2 ON
Full guide for Cabinet overheaton the Keston Celsius 25
Flame sensing electrodeGas valveIgnition leadCondensate trap
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