BoilerFaultCodes
The most common Grant faults
Your boiler has sensed a blockage or a pump failure that is stopping water from moving through the system properly.
Why it happens: This fault occurs when water is unable to flow freely through the boiler, leading to a sudden rise in internal pressure. The most common reason is a failed circulating pump that can no longer push water around your radiators, or a large pocket of air trapped within the pipework that is acting as a physical blockage.
Check that your radiator valves are openBleed your radiators to remove trapped airEnsure the system pressure gauge is within the correct range (usually 1.0 to 1.5 bar)
Your boiler has detected that the water pressure in the central heating system is too low to operate safely.
Why it happens: This fault occurs when the water level within your heating system drops below the minimum required for the boiler to heat up safely. The most common reason is a slow leak from a radiator valve or joint, though it often happens after you have bled air out of your radiators without refilling the system afterwards.
Locate the filling loop, which is usually a flexible silver hose beneath the boiler.Slowly open the small valves at either end of the hose until you hear water flowing.Watch the pressure gauge and close the valves tightly once the needle reaches between 1.0 and 1.5 bar.
Your boiler's main internal computer has encountered a processing error and cannot safely operate.
Why it happens: This fault occurs when the boiler's main control board experiences a critical electronic failure, meaning it can no longer communicate with the internal sensors or components. The most common reason is a component failure on the circuitry itself, often caused by age, a power surge, or moisture ingress affecting the delicate electronics.
Press the reset button on the control panel onceTurn the main power switch to the boiler off, wait 30 seconds, and turn it back onEnsure the boiler has not been subject to a recent power surge or lightning strike
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 has lost electrical power and cannot start any heating or hot water functions.
Why it happens: This fault occurs when the boiler is not receiving the electrical current required to operate its internal components. The most common reason is a simple blown 3-amp fuse in the fused spur switch or a tripped circuit breaker in your home's main consumer unit. In more serious cases, it can be caused by a surge that has damaged the boiler's main control board.
Check that the boiler's main power switch is turned to the 'ON' position.Inspect your home's main consumer unit (fuse box) to see if a circuit breaker has tripped.Check the fused spur switch (usually near the boiler) and replace the 3-amp fuse if it has blown.
Your boiler is not currently receiving a signal from your timer or thermostat telling it to switch on.
Why it happens: This occurs when there is a break in communication between your heating controls and the boiler. The most common reason is that your room thermostat or timer hasn't been set high enough to trigger a heat request, but it can also be caused by flat batteries in a wireless controller or a faulty receiver box failing to pass the signal through.
Check that your room thermostat is turned up higher than the current room temperature.Ensure your programmer or timer is set to 'ON' or 'AUTO'.Check if the batteries in your wireless thermostat need replacing.
Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit.
Why it happens: This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water coming back from your radiators. The most common reason is that the internal components of the sensor have failed or the electrical connection has become loose or corroded. Because the boiler cannot safely monitor the water temperature, it shuts down to prevent potential overheating.
Full guide for Vortex PP1Your boiler has detected a problem with a sensor that monitors the temperature of the exhaust gases, and it has likely stopped working as a safety precaution.
Why it happens: This fault occurs when the boiler's internal computer loses communication with the sensor that measures the temperature of the exhaust gases. The most common reason is that the sensor has developed an electrical fault or the wiring connecting it to the main control board has become loose or damaged. To ensure the appliance doesn't overheat or become unsafe, the boiler will automatically stop firing until the part is replaced.
Full guide for Vortex PP2