BoilerFaultCodesThe 6 most common faults
01
Power ON (Green LED) blinking High DIY-safe
Your boiler has stopped working because it doesn't have enough water inside the system to operate safely.
What to try first
Locate your boiler's filling loop, which is usually a silver braided hose connecting two pipes under the boiler.Open the valves on the filling loop to allow cold mains water into the system until the pressure gauge reads between 1 and 1.5 bar.Close the valves tightly and check the front panel to see if the blinking light has stopped.
02
Ignition lockout High Engineer
Your boiler has stopped working because it failed to light the flame, which often happens due to a simple supply issue or a temporary glitch.
Full guide for Ignition lockout03
Safety Lock-out LED High Engineer
Your boiler has stopped working because it failed to light or has become too hot, causing a safety shutdown to protect your home.
Full guide for Safety Lock-out LED04
Overheat thermostat High Engineer
Your boiler has automatically turned itself off because it got too hot, likely to prevent internal damage or overheating.
Full guide for Overheat thermostat05
Ignition Lock-out High Engineer
Your boiler has stopped working because it failed to light the flame, so it has purposefully shut down for safety.
Full guide for Ignition Lock-out06
Activate High Engineer
Your boiler has failed to ignite and cannot establish a flame, likely because it is not properly recognising its internal control settings or requires a part replacement.
Full guide for Activateon the Halstead Ace
Pressure relief valveFlow switchPressure gaugeIgnition electrodeGas valvePrinted Circuit Board (PCB)
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 Halstead 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