BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure is either too low or too high for it to operate safely, or the sensor that monitors this pressure has lost its connection.
Check the pressure gauge on the front of the boiler or via the digital display.If the pressure is below 1.0 bar, use the filling loop valves to carefully top up the system to 1.5 bar.If the pressure is above 3.0 bar, bleed a radiator to release excess water and pressure.Reset the boiler once the pressure is within the normal operating range (1.0 to 1.5 bar).
Your boiler has shut down because the internal water temperature has become too hot, usually caused by a circulation problem or a blockage.
Check that your radiator valves are open to allow water to flow.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.Check if your pump is running or if there is a noticeable blockage in the magnetic filter.
Your boiler has detected that the water pressure is too low for the system to run safely and has shut down to protect itself.
Locate the filling loop (the flexible silver hose) underneath or near the boiler.Slowly open the one or two taps/handles on the filling loop until you hear water moving.Watch the pressure gauge on the boiler screen until it reaches approximately 1.5 bar, then close the taps tightly.Reset the boiler using the 'Reset' button.
Your boiler is failing to light the fuel needed to provide heat and hot water, usually due to a lack of gas supply or a blocked condensation pipe.
Check that your gas emergency control valve is open and you have credit on your meter.Inspect the white plastic condensation pipe outside for ice and defrost it with warm water if frozen.Gently press the 'Reset' button on the boiler control panel for 2 seconds.
Your boiler has stopped because it thinks the water is heating up too quickly or flowing the wrong way, which usually means water isn't moving through the system properly.
Check that all radiator valves (TRVs) are turned to the highest settingEnsure the external heating pump (if present) is switched on and runningCheck that all isolation valves underneath the boiler are fully openRestart the boiler using the reset button
Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot heat your home or water safely.
Full guide for 20on the Atag iS System
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 Atag 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