BoilerFaultCodesThe 6 most common faults
01
E 08 High DIY-safe
Your boiler has detected that the water level inside the heating system is too low to operate safely.
What to try first
Locate the filling loop, which is usually a silver braided hose under the boiler connected to two valves.Slowly open the valves to allow mains water into your heating system.Watch the pressure gauge on the front of the boiler until it reaches the green zone, typically between 1.0 and 1.5 bar.Close both valves tightly and restart the boiler.
02
E04 High Engineer
Your boiler is trying to start but the flame is failing to ignite or stay alight, so it has shut down as a safety precaution.
Full guide for E0403
A 18 High Engineer
Your boiler is failing to stay lit because the flame keeps going out shortly after it starts.
Full guide for A 1804
A 37 High Engineer
Your boiler's main control computer is failing to communicate properly, which has caused the system to shut down for safety.
Full guide for A 3705
A 39 High Engineer
Your boiler's main internal computer has detected a critical electronic error that is preventing it from functioning correctly.
Full guide for A 3906
A 40 High Engineer
Your boiler's main computer control panel is experiencing an internal electronic failure, which is preventing the system from operating correctly.
Full guide for A 40on the Ariston Euro Prisma 24
Filling loopPressure relief valvePressure sensorIgnition electrodeGas valveCircuit 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 Ariston 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