BoilerFaultCodesThe 6 most common faults
01
E10 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is usually a flexible silver hose connected between two pipes under the boiler.Open the small valve(s) on the loop to allow water into the system while watching the pressure gauge on the front of the boiler.Close the valve(s) once the needle reaches the green zone, typically between 1.0 and 1.5 bar.
02
E01 High Engineer
Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.
Full guide for E0103
E02 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for E0204
E05 High Engineer
Your boiler's temperature sensor is faulty, which means the system cannot accurately read how hot the water is and has stopped working as a safety precaution.
Full guide for E0505
E16 High Engineer
Your boiler has detected that the internal fan is not operating correctly, which prevents it from safely venting gases, so it has shut down to protect your home.
Full guide for E1606
E24 High Engineer
Your boiler is struggling because it detects a confusing difference in temperature between the water leaving the unit and the water returning to it, so it has shut down to prevent damage.
Full guide for E24on the Alpha CB28
Filling loopPressure relief valvePressure sensorIgnition electrodeGas valvePrinted Circuit Board (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 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