BoilerFaultCodesThe 6 most common faults
01
Neon A and B Flashing on and off alternatively High DIY-safe
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.
What to try first
Locate the filling loop under your boiler or near the hot water cylinder.Open the valves slowly to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves firmly and check the boiler display or reset the unit if necessary.
02
Neon B Flashing on and off High Engineer
Your boiler has detected an issue with its internal temperature measuring system, so it has temporarily stopped working to keep things safe.
Full guide for Neon B Flashing on and off03
Neon A Illuminated continuously High Engineer
Your boiler has stopped working because the burner failed to ignite, meaning you currently have no heating or hot water.
Full guide for Neon A Illuminated continuously04
Neon A Illuminated continuously and B flashing High Engineer
Your boiler is struggling to circulate water properly, which usually means the water isn't flowing freely around the system.
Full guide for Neon A Illuminated continuously and B flashing05
Neon A Flashing on and off Emergency Engineer
Your boiler has automatically shut down because it detected dangerously high temperatures inside the unit.
Full guide for Neon A Flashing on and off06
Neon A and B Flashing on and off at the same time Emergency Engineer
Your boiler has detected an issue with safely removing exhaust gases outside, so it has locked itself out to prevent any risk.
Full guide for Neon A and B Flashing on and off at the same timeon the Alpha HETEC
Filling loop valvePressure relief valvePressure gaugeNTC thermistor / temperature sensorWiring harnessIgnition 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 Alpha 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