BoilerFaultCodesThe 6 most common faults
01
13 High DIY-safe
Your boiler has been manually reset too many times in a single hour and has locked itself as a safety precaution.
What to try first
Locate the main electrical power switch for the boiler (usually a fused spur near the unit).Switch the power OFF.Wait approximately 30 seconds.Switch the power back ON to clear the lockout.
02
21 High Engineer
Your boiler's main control panel has developed an internal electrical error and can no longer process information correctly.
Full guide for 2103
25 High Engineer
Your boiler's internal computer parts are having trouble communicating because their software versions do not match.
Full guide for 2504
26 High Engineer
Your boiler is struggling to keep its burner lit and has shut down for safety after failing to maintain a flame multiple times.
Full guide for 2605
30 High Engineer
Your heater has detected a technical fault with its internal temperature sensor, causing the system to shut down for safety.
Full guide for 3006
31 High Engineer
Your boiler has lost connection with its internal air temperature sensor, which means it cannot safely monitor the heat level and has stopped working.
Full guide for 31on the Johnson Starley C10d
None (Software reset)Control PCB (if fault persists)ESYS Control BoardMain PCBESYS Electronic Control BoardFlame sensing electrode
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 Johnson Starley 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