BoilerFaultCodesThe 6 most common faults
Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.
Why it happens: This fault occurs when the temperature sensor inside your hot water storage tank detects that the water has dropped to a near-freezing level. To protect the internal components from being damaged by expanding ice, the boiler temporarily pauses operation until the water temperature rises to a safe level. This is typically caused by extremely cold incoming mains water or a storage tank located in an unheated area like a garage or loft.
Full guide for F1Your boiler has detected that the water pressure inside the system has dropped too low to operate safely.
Locate the filling loop (usually a silver braided hose with valves underneath the boiler).Open the valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves firmly and check for any leaks.
Your boiler's electronic control centre has detected an internal communication error and has shut down for safety.
Full guide for F11Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage to its internal parts.
Full guide for F20Your boiler has detected that the water inside the system is not circulating properly, meaning heat is not being moved from the boiler to your radiators or taps efficiently.
Full guide for F23Your boiler is struggling to push water around your heating system correctly, which is causing it to shut down to protect itself from overheating.
Full guide for F24on the Glow-worm Ultracom sxi
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 Glow-worm 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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