BoilerFaultCodesThe 6 most common faults
01
13 High Engineer
Your boiler has disabled the reset button because it was pressed too many times in a short period, likely due to an underlying fault causing repeated lockouts.
Full guide for 1302
21 High Engineer
Your boiler’s internal computer is having trouble processing signals from its electronic sensors, which has caused the system to stop working for safety.
Full guide for 2103
25 High Engineer
Your boiler's internal computer parts are having trouble communicating because they are running mismatched software programs.
Full guide for 2504
26 High Engineer
Your boiler is repeatedly struggling to keep the flame lit and has safely shut down to prevent damage.
Full guide for 2605
30 High Engineer
Your boiler has detected a fault with the sensor that monitors air temperature within the ducting, causing it to stop running for safety.
Full guide for 3006
31 High Engineer
Your boiler has lost its connection to the sensor that monitors air temperature inside the ducting, causing the system to stop working for safety.
Full guide for 31on the Johnson Starley C16u
Ignition LeadSpark ElectrodeFlame Sensing ProbeGas ValveMain PCB (Printed Circuit Board)Wiring harness
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