BoilerFaultCodesThe 6 most common faults
01
F9 High Engineer
Your boiler's air circulation system has stopped working, meaning the unit cannot safely ignite to provide you with heating or hot water.
Full guide for F902
F4 High Engineer
Your boiler is failing to light because it cannot detect a flame, which means your heating and hot water have stopped working.
Full guide for F403
30 High Engineer
Your boiler has stopped working because it is unable to accurately measure its own internal temperature due to an electrical connection issue.
Full guide for 3004
38 High Engineer
Your boiler has stopped working because it has lost the electronic signal from the sensor that monitors the water temperature, causing it to shut down for safety.
Full guide for 3805
51 High Engineer
Your boiler has stopped producing hot water because a sensor that measures water temperature is reporting a faulty electrical signal.
Full guide for 5106
52 High Engineer
Your boiler has detected an electrical fault with the sensor that measures the flow of water, causing it to shut down for safety.
Full guide for 52on the Viessmann Vitodens 050-W BPJD
Fan unitWiring harnessControl boardIgnition electrodeIonisation probeGas valve
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