BoilerFaultCodesThe 6 most common faults
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.
Locate the filling loop valves underneath your boiler or near the hot water cylinder.Open the valves slowly to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the filling loop valves tightly and press the reset button on your boiler.
Your boiler has detected that water is struggling to flow through the system properly, which may be due to trapped air or a blockage.
Check your boiler pressure gauge and top up the system to 1.5 bar if it is low.Bleed all radiators in your home starting from the bottom floor to ensure no air is trapped in the system.Restart the boiler using the reset button or power cycle it at the fused spur.
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.
Locate the filling loop or internal filling valves connected to your boiler.Open the valves slowly to allow water into the system while watching the pressure gauge.Stop filling once the needle reaches between 1.0 and 1.5 bar, then securely close the valves.
Your boiler has detected an internal computer error and needs to be restarted.
Locate the reset button or power switch on your boiler.Turn the boiler off, wait for 30 seconds, and turn it back on.Attempt to reset the system to see if normal operation resumes.
Your boiler has detected an issue with the internal fan that safely pushes waste gases outside, causing it to lock out for your safety.
Full guide for F9Your boiler has detected an issue with its internal ignition control system and has safely stopped working to prevent any risk.
Full guide for EEon the Viessmann Vitodens 242-F FB2B
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 Viessmann 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