BoilerFaultCodesThe 6 most common faults
Your boiler has detected that water is not moving through the system quickly enough to prevent it from overheating.
Why it happens: This fault occurs when the water inside the boiler heats up too quickly because it isn't being pumped away into your radiators or cylinder fast enough. The most common reasons are a failing external pump, a blockage caused by sludge in the pipework, or air trapped within the system preventing a steady flow.
Check that all radiator valves are fully openEnsure the external heating pump (if visible) is runningCheck that the system water pressure is within the green zone on the gaugeReset the boiler using the selector switch
Your boiler has lost its connection with the thermostat or control panel, meaning it cannot receive instructions to turn on or off.
Why it happens: This fault occurs when the boiler and your thermostat can no longer 'talk' to each other, often due to physical interference or a hardware failure. The most common reason is that the batteries in your room thermostat have died or the wireless receiver attached to the boiler has lost its signal. In some cases, it may be caused by a faulty circuit board that is unable to process incoming signals from your controls.
Check if the batteries in your Alpha Climatic room thermostat need replacing.Ensure the thermostat is within range of the boiler and has not been moved.Try restarting the boiler using the reset button to refresh the connection.
Your boiler is overheating because the water is not flowing through the system as quickly as it should.
Why it happens: This fault occurs when the water inside the boiler heats up too quickly because it isn't being moved away into your radiators fast enough. The most common reasons are a failing external pump, a blockage in the pipework, or a buildup of debris and limescale inside the heat exchanger that restricts water flow.
Check that all radiator valves (TRVs) are fully openEnsure the external system pump is running and hasn't seizedCheck for any blockages in the system filters
Your boiler has stopped running because an external safety thermostat has detected that the water temperature has become too hot.
Why it happens: This fault occurs when an external safety device triggers to prevent the system from getting dangerously hot. It usually happens because water is not moving through the boiler quickly enough, often due to a pump failure or a blockage in the heating pipes. When the heat cannot be carried away from the boiler, the temperature spikes and the safety thermostat cuts the power to prevent damage.
Check that your pump is running and hasn't seizedEnsure all radiator valves and boiler service valves are fully openPress the 'Reset' button on the front of the boiler control panel
Your boiler has shut down because the water returning from your radiators has become too hot, usually caused by a circulation problem.
Why it happens: This fault occurs when the water coming back into the boiler from your heating system is much hotter than it should be, suggesting the heat isn't being distributed to your radiators. The most common reason is that the internal pump has failed or is struggling to push water through the pipes, causing heat to build up inside the unit. In some cases, a blockage in the system or a faulty temperature sensor can also trigger this safety shutdown.
Check that at least two or three radiators have their valves turned fully openEnsure your central heating pump is running and hasn't seizedCheck the system pressure gauge and top up to 1.5 bar if it is low
Your boiler has stopped running because it senses that even though the burner is lit, the water inside isn't getting any warmer.
Why it happens: This fault occurs when the boiler fires up but the sensors do not detect a sufficient rise in water temperature, causing the system to shut down for safety. The most common reason is that the water isn't moving through the unit properly, often due to a failed internal pump or a blockage in the pipework. It can also signify that the sensors responsible for measuring heat are faulty or that the main heat exchanger is clogged with debris.
Check that the radiator valves and the main isolation valves under the boiler are fully open.Ensure your system pressure is topped up to between 1 and 1.5 bar.Try resetting the boiler to see if the error was caused by a temporary air lock.
on the Alpha E-Tec Regular
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 Alpha 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