BoilerFaultCodesThe 6 most common faults
Your boiler was working but has suddenly turned off because the flame has gone out and it cannot manage to relight itself.
Why it happens: This fault occurs when the boiler successfully starts but lose its flame while it is trying to heat your home or water. The most common reasons are a temporary interruption in the gas supply, a blocked flue, or internal components like electrodes becoming too dirty to detect the flame. It can also be caused by a buildup of debris in the condensate trap preventing the burner from staying lit.
Check if other gas appliances, like a hob, are still working to ensure your gas supply hasn't been interrupted.If it is freezing outside, check the condensate pipe (the plastic pipe leading outside) for ice and defrost it with warm water.Press the reset button (a flame symbol with a cross through it) for five seconds to see if the boiler restarts.
Your boiler has detected an issue with the gas valve or the way it is communicating, meaning it cannot safely start up to provide heat or hot water.
Full guide for F.93Your boiler has detected an issue with the type of gas it is receiving, meaning it has shut itself down to prevent unsafe operation.
Full guide for F.92Your boiler has detected an issue with the gas flow, meaning it cannot safely ignite or maintain a flame to heat your home.
Full guide for F.53Your boiler is having trouble communicating with the separate hot water storage tank, which may result in a loss of hot water.
Full guide for F.91on the Vaillant ecoTEC plus 612
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 Vaillant 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