BoilerFaultCodesThe 6 most common faults
01
E01 High DIY-safe
Your boiler's burner has stopped working because it cannot light the fuel, meaning your heating and hot water have turned off for safety.
What to try first
Check that your heating oil tank has enough fuelEnsure the oil supply valve is fully openPress the illuminated reset button on the burner once to try and restart the system
02
E04 High DIY-safe
Your boiler has detected that there is not enough water pressure in the system to operate safely, which is often caused by a small leak or after bleeding your radiators.
What to try first
Locate the pressure gauge on the front of the boiler or under the casing.Check if the needle is below 1 bar (usually in the red zone).Use the external filling loop to top up the water pressure until the gauge reads between 1 and 1.5 bar.
03
E02 High Engineer
Your boiler has overheated, causing a safety switch to trigger and shut down the system to prevent damage.
Full guide for E0204
E05 High Engineer
Your boiler has lost its ability to monitor the temperature of the water leaving the unit, meaning it cannot operate safely to provide heating or hot water.
Full guide for E0505
E06 High Engineer
Your boiler's hot water sensor has stopped working correctly, which means the system cannot safely monitor the temperature of the water going to your taps.
Full guide for E0606
E12 High Engineer
Your boiler has lost communication with its hot water temperature sensor, meaning it cannot safely monitor or heat your water tank.
Full guide for E12on the Warmflow Agentis Internal
Oil nozzleOil pumpPhotocellFlexible oil hoseFilling loop valveExpansion vessel
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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