BoilerFaultCodesThe 6 most common faults
01
Er 04 High DIY-safe
Your boiler has detected that water is not flowing properly around your heating system, usually because the pressure is too low or a pump has stopped working.
What to try first
Check the pressure gauge on the front of your boiler; if it is below 1.0 bar, use the filling loop to top it up to between 1.0 and 1.5 bar.Ensure your heating controls and thermostat are calling for heat.Restart the boiler using the reset button or dial.
02
04E High DIY-safe
Your boiler has detected that there is not enough water circulating inside it to work safely, so it has shut down to prevent damage.
What to try first
Check the pressure gauge on the front of the boiler; if it is below 1 bar, your system needs topping up.Locate the external filling loop (or internal key) usually found underneath the boiler.Slowly open the valve to let water into the system until the gauge reads between 1 and 1.5 bar, then tighten the valve firmly.
03
Er 01 High Engineer
Your boiler has failed to light the flame and has turned itself off for safety reasons, meaning you currently have no heating or hot water.
Full guide for Er 0104
Er 02 High Engineer
Your boiler has detected that it has become dangerously hot and has automatically shut down to prevent damage or overheating.
Full guide for Er 0205
Er 03 High Engineer
Your boiler has detected a general internal fault that has caused it to shut down for safety reasons.
Full guide for Er 0306
Er 05 High Engineer
Your boiler is unable to safely clear exhaust gases because the internal fan mechanism is not responding correctly.
Full guide for Er 05on the Biasi Advance Plus 16S 25S 30S
Circulating pumpFlow sensorPressure sensorCirculation pumpPressure relief valveIgnition electrode
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 Biasi 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