BoilerFaultCodesThe 6 most common faults
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 is struggling to manage the temperature of its internal hot water store, meaning you likely have no hot water available.
Why it happens: This fault occurs when the boiler's internal computer loses communication with the sensor that monitors the temperature of your stored hot water. The most common reason is that the sensor has developed an electrical fault or the wiring has vibrated loose, preventing the boiler from knowing when to safely heat the water. In rarer cases, the main control board itself may be failing to process the signals it receives.
Full guide for DHW pumpYour boiler is not detecting that a hot tap has been turned on, which is preventing it from heating your water.
Why it happens: This fault occurs when the boiler fails to detect water moving through the pipes when you turn on a hot tap. The most common reason is that the internal sensor used to trigger the burner has become stuck or damaged, preventing the boiler from knowing there is a demand for hot water. In some cases, a perished rubber diaphragm or a blockage within the unit is stopping the mechanical parts from moving correctly.
Full guide for FlowYour boiler has stopped working because the amount of water inside your heating system has dropped too low.
Locate the external filling loop, which is a flexible silver hose connected to two valves under the boiler.Slowly open both valves to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly and ensure the boiler resets itself.
Your boiler has stopped working because the water pressure inside your heating system has dropped too low.
Locate the external filling loop, usually found underneath the boiler.Open the small valve(s) to allow mains water into the system while watching the pressure gauge.Stop filling once the needle reaches the green zone, typically between 1.0 and 1.5 bar.Ensure the valve is fully closed tightly to prevent over-pressurisation.
on the Grant Vortex Pro Combi 26
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