BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water returning from your radiators is significantly hotter than the water leaving the boiler, suggesting the water isn't flowing correctly.
Ensure all radiator valves (TRVs) are turned to the highest settingCheck that at least one radiator or bypass valve is fully openBleed all radiators to remove trapped air locks
Your boiler has stopped working because the water returning from your radiators is significantly hotter than the water being sent out, suggesting a blockage or a pump problem is preventing proper circulation.
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1 and 1.5 bar on the gaugeGently bleed your radiators to remove any trapped airRestart the boiler using the Reset button
Your boiler has lost water pressure and has shut down to prevent damage, meaning it simply needs to be refilled to the correct level.
Locate the filling loop (usually blue handles or a small plastic key) underneath the boiler.Slowly open the valves until you hear water entering the system.Watch the pressure gauge and close the valves tightly once it reaches 1.5 bar.The error code should clear automatically; if not, press the 'Reset' button.
Your boiler has tried to light several times but has failed to create a flame, meaning you currently have no heating or hot water.
Check if your home gas supply is active by testing another gas appliance like a hob.Verify that your gas prepaid meter (if applicable) has enough credit.If it is freezing outside, check that the white plastic condensate waste pipe is not frozen.Hold the 'Reset' button for five seconds to see if the boiler restarts.
Your boiler has too much water pressure inside the system, causing it to shut down for safety.
Check that the filling loop valves under the boiler are tightly closed.Bleed water from a radiator using a bleed key until the pressure gauge on the boiler falls back between 1 and 1.5 bar.Restart the boiler once the pressure is stabilised.
Your boiler has detected that the safety sensor for an underfloor heating circuit has tripped to prevent the floor from overheating.
Full guide for 116on the Ariston Clas ONE 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 Ariston 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.
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