BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because it has detected an unsafe build-up of heat or a lack of water flow, triggering a safety cut-out to prevent damage.
Check that your central heating pressure is between 1.0 and 1.5 barEnsure all radiator valves are fully open to allow water flowOnce the boiler has cooled down, press the 'Reset' button on the control panel
Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.
Locate the filling loop (usually a silver braided hose with one or two small valves) underneath the boiler.Slowly open the valve(s) until you hear water entering the system and watch the pressure gauge.Close the valves tightly once the pressure reaches between 1.0 and 1.5 bar, then reset the boiler.
Your boiler has lost communication with your smart thermostat or heating controller and cannot receive instructions to heat your home.
Check that your wall-mounted thermostat is switched on and has working batteries.Ensure any wireless receiver plugged into or near the boiler has a power light on.Try restarting your internet router if your OpenTherm controller relies on a bridge or hub connection.
The boiler has automatically shut down because it became too hot, but it will attempt to restart itself once it has cooled down.
Check that your home's thermostat is turned downEnsure all radiator valves are fully open to allow water to circulateCheck the boiler pressure gauge and top up to 1.5 bar if it is too lowWait for the boiler to cool down and see if it restarts automatically
Your boiler is not receiving enough gas to light properly, which means it cannot provide heating or hot water.
Check if other gas appliances, like a hob, are working to confirm your gas supply is active.If you have a pre-payment meter, ensure it has sufficient credit.Check that the gas emergency control valve (usually located near the meter) is in the fully open position.Reset the boiler by following the instructions on the display panel.
Your boiler is trying to start but cannot detect a flame, which prevents it from firing up to provide heating or hot water.
Check that your gas emergency control valve is in the 'on' position.Verify if other gas appliances in your home, such as a hob, are working correctly.If you have a pre-payment meter, ensure you have sufficient credit.Press the 'Reset' button on the boiler control panel once.
on the Viessmann Vitodens 100-W B1GA
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 Viessmann 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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