BoilerFaultCodesThe 6 most common faults
01
118 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
What to try first
Locate the external filling loop, usually a silver braided hose with one or two valves underneath the boiler.Slowly open the valve(s) to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valve(s) firmly and ensure the boiler resets itself.
02
20 High Engineer
Your boiler has detected an internal communication error between its internal parts, meaning it has safely shut itself down to prevent potential damage.
Full guide for 2003
28 High Engineer
Your boiler is struggling to read its own internal water temperature correctly, which is preventing it from heating your home or water safely.
Full guide for 2804
40 High Engineer
Your boiler has detected a general internal fault that is preventing it from starting up correctly.
Full guide for 4005
160 High Engineer
Your boiler has detected a problem with the fan or its internal electronics, meaning it has safely shut itself down to prevent further issues.
Full guide for 16006
321 High Engineer
Your boiler has detected an internal issue with one of its main sensors, meaning it cannot operate safely and has shut itself down.
Full guide for 321on the Baxi Assure
Filling loopPressure relief valvePressure sensorPrinted Circuit Board (PCB)Wiring harnessGas 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 Baxi 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
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