BoilerFaultCodesThe 6 most common faults
01
0.5bar High DIY-safe
Your boiler has lost pressure, which means there isn't enough water inside the system to circulate heat throughout your home.
What to try first
Locate the filling loop, which is usually a flexible silver hose with one or two valves underneath your boiler.Open the valves slowly to allow mains water into the system while watching the pressure gauge on the front of your boiler.Close the valves firmly once the needle on the gauge reaches between 1.0 and 1.5 bar.
02
01 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 0103
02 High Engineer
Your boiler is struggling to clear exhaust fumes safely, so it has shut down to prevent any risk of fumes entering your home.
Full guide for 0204
05 High Engineer
Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent any damage or danger.
Full guide for 0505
06 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the water used for your radiators, causing it to stop heating as a safety precaution.
Full guide for 0606
09 High Engineer
Your boiler is struggling to accurately detect the water pressure inside the system, which is preventing it from safely starting up.
Full guide for 09on the Saunier Duval Thelia
Filling loopPressure relief valveExpansion vesselIgnition electrodeGas valveIgnition transformer
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 Saunier Duval 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