BoilerFaultCodesThe 5 most common faults
01
A1 High DIY-safe
Your boiler has detected that there isn't enough water moving through the system, which is usually caused by a leak or a pump that has become stuck or worn out.
What to try first
Check the pressure gauge on the fascia and top up to 1.5 bar if it is lowLook for any visible water leaks under the boiler or around your radiatorsCheck that all radiator valves and internal isolation valves are fully open
02
EA High DIY-safe
Your boiler has stopped working because it cannot light the fuel required to provide heating and hot water.
What to try first
Check if your gas or oil supply is turned on and that you have credit on your meterPress and hold the reset button for five seconds to see if the boiler restartsThaw your external condensate pipe with warm water if it is frozen during cold weather
03
A7 High Engineer
Your boiler's temperature sensor for hot water is broken or has a loose connection, which means the system cannot correctly measure how hot your water is.
Full guide for A704
A8 High Engineer
Your boiler has lost its connection to the external heating controls, meaning it cannot receive instructions on when to turn the heating or hot water on.
Full guide for A805
FA Emergency Engineer
Your boiler is seeing a flame when it should be turned off, which means the fuel supply might not be closing properly.
Full guide for FAon the Worcester Bosch Heatslave
Central heating pumpAuto air ventInternal pipe sealsIgnition ElectrodeFlame SensorGas 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 Worcester Bosch 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