BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because it has detected an unsafe build-up of heat inside the unit.
Check that all radiator valves are fully open to allow water flow.Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge.Wait for the boiler to cool down and press the 'Reset' button.
Your boiler has detected that the water pressure is too low to operate safely, causing it to shut down to prevent damage.
Locate the filling loop (usually a silver flexible hose) underneath your boiler.Slowly open the small valve(s) to allow water into the system.Watch the pressure gauge and close the valve(s) once it reaches 1.5 bar.The fault code should disappear, allowing the boiler to restart.
Your boiler has detected that the water pressure is too low for it to operate safely and effectively.
Locate the filling loop (usually a silver braided hose underneath the boiler).Slowly open the valve or valves until you hear water entering the system.Monitor the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar.
Your boiler is struggling to move water through the system, which causes it to shut down to prevent overheating.
Check if the boiler pressure is between 1.0 and 1.5 barEnsure all radiator valves and external isolation valves are fully openBleed all radiators to remove trapped air pockets
Your boiler is overheating because water isn't flowing through the system quickly enough to take the heat away.
Check that your boiler pressure gauge is between 1.0 and 1.5 barEnsure all radiator valves and the boiler isolation valves are fully openBleed your radiators to remove any trapped air pockets
Your boiler has switched itself off because it has detected that the water inside has become dangerously hot.
Check that all radiator valves are fully open to allow water to flow.Ensure there is enough water pressure in the system by checking the gauge.Try resetting the boiler carefully once the unit has cooled down.
on the Unical Alkon C 28 HE
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 Unical 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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
Affiliate links. We may earn a commission at no extra cost to you.