BoilerFaultCodesThe 5 most common faults
01
Red Neon on fascia High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
What to try first
Locate the filling loop (usually a silver braided hose with one or two valves near the boiler piping).Slowly open the valve(s) to allow water to enter the system while watching the pressure gauge.Stop when the needle reaches the green zone (typically between 1.0 and 1.5 bar) and ensure both valves are tightly closed.
02
Neon 1 High Engineer
Your boiler is failing to start because it is not detecting electricity or there is not enough water pressure inside the system to operate safely.
Full guide for Neon 103
Neon 2 High Engineer
Your boiler has automatically shut down because it has detected that it is getting too hot inside, likely because the water is not circulating as it should.
Full guide for Neon 204
Neon 3 High Engineer
Your boiler is failing to clear combustion gases properly, so it has safely shut down to prevent any risk.
Full guide for Neon 305
Neon 4 High Engineer
Your boiler is failing to light the flame needed to heat your water or home, causing the system to shut down for safety.
Full guide for Neon 4on the Glow-worm Space Saver Compleheat 30 40 50
Filling loopPressure gaugePressure relief valvePCB fusePressure switchControl 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 Glow-worm 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