BoilerFaultCodesThe 6 most common faults
01
Burner lock-out High DIY-safe
Your boiler has detected a temporary issue with the burner and has safely shut itself down to prevent any damage.
What to try first
Check your oil tank to ensure you have enough fuel and that the supply valve is openWait 60 seconds for the internal control unit to resetGently press the illuminated red reset button located on the burner once
02
Boiler will not start High DIY-safe
Your oil boiler is failing to start up because it is not receiving power or fuel, or the burner itself is not firing.
What to try first
Check that the boiler's main power switch and any external spur switches are turned on.Verify that you have an adequate supply of heating oil in your storage tank.Press the burner lockout reset button on the boiler once, but do not repeatedly press it if it fails again.
03
Boiler operating on overheat thermostat High Engineer
Your boiler has temporarily shut down because the internal safety thermostat detected that it was getting too hot.
Full guide for Boiler operating on overheat thermostat04
Visible smoke from flue or high smoke number Emergency Engineer
Your boiler is producing visible smoke from the flue, which means the fuel is not burning cleanly and needs immediate professional attention.
Full guide for Visible smoke from flue or high smoke number05
Fumes and puffing during starting Emergency Engineer
Your boiler is struggling to breathe properly when it tries to start up, which can cause smoke, soot, or a puffing sound.
Full guide for Fumes and puffing during starting06
Oil odours Emergency Engineer
Your Grant boiler is letting out an oil smell, which usually means there is a small leak somewhere in the fuel supply pipework.
Full guide for Oil odourson the Grant Vortex 20-26
PhotocellIgnition electrodesOil nozzleControl boxBurner Control BoxOil Solenoid 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 Grant 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