BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has reached an unsafe temperature to protect the internal components from damage.
Check that all radiator valves are fully open to allow water to circulateEnsure the boiler pressure gauge is between 1 and 1.5 barPress the reset button once to see if the fault clears after the system has cooled down
Your boiler has shut down because the water inside the central heating system has reached an unsafely high temperature.
Check that all radiator valves are fully openEnsure the boiler pressure gauge is between 1.0 and 1.5 barSwitch the boiler off and back on again to reset the system after it has cooled down
Your boiler has detected that water isn't flowing through the system properly, which has caused it to shut down to prevent overheating.
Check that all radiator valves are fully open.Check your boiler pressure gauge to ensure it is between 1 and 1.5 bar, and top it up using the filling loop if it is too low.Restart or reset the boiler to see if the error clears.
Your boiler is failing to light the internal flame needed to produce heat or hot water.
Full guide for F1Your boiler is failing to light its burner, which means it cannot produce any heating or hot water for your home.
Full guide for F4Your boiler is struggling to clear exhaust gases safely, so it has shut down to prevent any risk of fumes entering your home.
Full guide for F2on the Saunier Duval SD Isotwin Condens F35 E
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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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