BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure inside your heating system is too low, meaning it needs to be topped up with more water to work correctly.
Locate the external filling loop, which is usually a flexible silver braided hose connecting two pipes near the boiler.Open the valves at both ends of the filling loop to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves firmly and ensure the filling loop is disconnected if required by your specific installation.
Your boiler has stopped working because the water pressure inside the system has dropped too low and needs to be topped up.
Locate the external filling loop, which is a small silver braided hose connecting two pipes near your boiler.Open the valves at both ends of the hose to allow mains water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly to stop the flow of water and ensure the pressure gauge stays steady.
Your boiler has stopped working because the water pressure inside the system has become too high, which is a safety mechanism to prevent damage.
Locate a radiator bleed valve and use a key to release water into a container until the pressure gauge drops to 1.5 bar.Alternatively, use a drain-off valve at a low point in the system to remove excess water.Check that the filling loop valves are fully closed and not passing water into the system.
Your boiler has detected that the water pressure inside the system is too low for it to operate safely.
Locate the filling loop, which is a silver braided hose with one or two valves connecting your cold water mains to your heating pipes.Slowly open the valve(s) to allow water into the system while watching the pressure gauge on the front of the boiler.Stop filling once the needle on the gauge reaches the green zone, typically between 1.0 and 1.5 bar, then tightly close the valves.
Your boiler is confused because two temperature sensors have been incorrectly identified or swapped, preventing it from safely heating your water.
Full guide for C10Your boiler has detected that the temperature sensors monitoring the water flow have been installed in the wrong positions or are providing conflicting information.
Full guide for C12on the Atag Premier
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