BoilerFaultCodesThe 6 most common faults
01
On Flash Flash High DIY-safe
Your boiler has detected that there is not enough water inside the system to operate safely and has shut down to prevent damage.
What to try first
Check your pressure gauge located on the boiler or near your pipes.If the reading is below 1 bar, locate your external filling loop (a silver braided hose connecting two pipes).Open the valves on the filling loop to allow water into the system until the gauge reaches 1.5 bar.Close the valves tightly and restart the boiler.
02
Reset light High DIY-safe
Your boiler has stopped working and needs a manual restart to try and clear a temporary internal error.
What to try first
Check the pressure gauge on the front of the boiler is between 1 and 1.5 barTurn the boiler switch to the 'Standby' positionPress and hold the reset button for 10 seconds, release it, then switch the boiler back to 'On'
03
On Off On High Engineer
Your boiler has failed to light the flame and has turned itself off for safety reasons.
Full guide for On Off On04
Flash Off On High Engineer
Your boiler has switched itself off because it has detected that its internal temperature has become dangerously high.
Full guide for Flash Off On05
Flash Flash On High Engineer
Your boiler has stopped working because it cannot properly move the gases required for combustion to safely leave the system.
Full guide for Flash Flash On06
On Flash On High Engineer
Your boiler has stopped working because a sensor that measures water temperature is providing an incorrect reading or has failed, causing the system to shut down for safety.
Full guide for On Flash Onon the Potterton Promax HE
Pressure relief valveExpansion vesselPressure sensorIgnition leadPrinted Circuit Board (PCB)Flame rectification 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 Potterton 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