BoilerFaultCodesThe 6 most common faults
Your boiler's burner has detected light when it should be dark inside, causing it to shut down for safety.
Why it happens: This fault occurs when the boiler's internal light sensor detects a flame or light source before the ignition process has even started. The most common reasons are a faulty sensor sending a false signal, a leaking fuel valve allowing a stray flame to persist, or light leaking into the burner housing through damaged seals.
Check that the burner cover and all casing panels are securely fitted and not letting in external light.Inspect the clear plastic viewing window for damage or missing seals.Press the reset button on the burner control box once all covers are tightened.
Your boiler's safety sensor thinks there is a fire inside before it has even started, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler's internal sensor detects light or a signal that looks like a fire before the burner has actually started. This is usually caused by a dirty sensor lens, a faulty control box, or a leaking fuel valve that is letting a small amount of oil onto the burner head.
Full guide for Red blinking lightYour boiler has stopped working because it cannot detect a flame or is struggling to ignite the fuel properly.
Why it happens: This fault happens when the boiler's internal computer can no longer detect a flame, causing it to shut down for safety. The root cause is typically a dirty light sensor that cannot 'see' the fire, or a mechanical failure in the parts that deliver the oil and spark needed to create the flame.
Full guide for Red steady onYour boiler is struggling to burn fuel correctly because the balance of air is incorrect or a sensor is faulty.
Why it happens: This fault occurs when the boiler's internal computer detects that the flame is not burning steadily or efficiently. It is usually caused by a blockage in the fuel nozzle, a worn-out component in the air supply system, or a dirty sensor that can no longer 'see' the flame effectively. When the air and fuel mix is incorrect, the boiler enters a safety mode to prevent damage or soot build-up.
Full guide for Green blinking lightYour boiler has detected too much pressure inside the system because the water isn't moving around properly or there is trapped air.
Check the pressure gauge and bleed your radiators to release any trapped air.Ensure all radiator valves and isolation valves are fully open.Restart the boiler once air is removed and pressure is topped up to the correct level.
Your boiler has detected that there is not enough water in the system to operate safely, which has caused it to shut down.
Locate the silver braided filling loop usually found underneath or near the boiler.Slowly open the valve(s) to allow water into the system while watching the pressure gauge.Close the valve(s) tightly once the gauge reaches between 1.0 and 1.5 bar.
on the Grant Vortex Blue
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