BoilerFaultCodesThe 6 most common faults
01
E01 High DIY-safe
Your boiler's burner has shut down because it cannot light the fuel, likely due to an empty oil tank or a blockage in the supply line.
What to try first
Check your oil tank level to ensure you have not run out of fuel.Inspect the oil supply valves to ensure they are fully open.Locate and press the illuminated reset button on the burner unit within the external cabinet.
02
E04 High DIY-safe
Your boiler has detected that the water pressure is too low for it to operate safely, which often happens after bleeding radiators or if there is a small leak.
What to try first
Locate the filling loop (the flexible silver hose) underneath or near the boiler.Slowly open the valve(s) until you hear water flowing and the pressure gauge rises to between 1.0 and 1.5 bar.Close the valve(s) tightly and restart the boiler to clear the fault.
03
E02 High Engineer
Your boiler has switched itself off because it has detected that the water inside has become too hot.
Full guide for E0204
E05 High Engineer
Your boiler has lost connection with a internal temperature sensor, meaning it cannot safely tell how hot the water is and has shut down as a precaution.
Full guide for E0505
E06 High Engineer
Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning the system cannot safely heat water for your taps.
Full guide for E0606
E12 High Engineer
Your boiler has lost communication with the temperature sensor that monitors your hot water tank, meaning it cannot safely heat your water.
Full guide for E12on the Warmflow Agentis External
Oil pumpPhotocellOil nozzleFuel filterExpansion vesselPressure relief valve
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 Warmflow 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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