BoilerFaultCodesThe 6 most common faults
01
118 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to try first
Locate the external filling loop or internal key under the boilerSlowly open the valves to allow mains water to enter the systemWatch the pressure gauge on the front of the boiler until the needle reaches the green zone between 1.0 and 1.5 barClose the valves firmly and check that the fault code has cleared
02
20 High Engineer
Your boiler is struggling to control its internal gas supply, which means it has safely shut itself down to prevent any risk of incomplete combustion.
Full guide for 2003
28 High Engineer
Your boiler is struggling to control the gas supply it needs to stay lit, so it has shut down to keep your home safe.
Full guide for 2804
40 High Engineer
Your boiler is struggling to manage the gas supply required to light the flame and heat your water, which has caused it to shut down for safety.
Full guide for 4005
160 High Engineer
Your boiler has detected an issue with the system that controls the flow of gas, meaning it has shut itself down to keep your home safe.
Full guide for 16006
321 High Engineer
Your boiler is having trouble controlling the flow of gas needed to stay lit, so it has shut down as a safety precaution.
Full guide for 321on the Main Eco Compact Combi
Filling loopPressure relief valvePressure sensorGas valvePCB (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 Main 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
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