BoilerFaultCodesThe 6 most common faults
Your boiler's control panel and its internal computer are not talking to each other, meaning the unit cannot receive instructions to provide heat or hot water.
Why it happens: This fault occurs when the data link between the boiler's control screen and its main internal computer is broken or interrupted. The most common reason is a loose wiring connection or a component failure caused by a power surge or natural wear and tear. Without this communication link, the boiler cannot process your heating requests and shuts down for safety.
Full guide for conYour boiler has detected that the water pressure inside the system has dropped too low, so it has safely shut itself down to prevent any damage.
Locate the filling loop (a silver flexible hose or internal key) underneath your boiler.Slowly open the valve to allow water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valve tightly and check that the error code clears from the display.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the filling loop (usually two silver taps connected by a flexible braided hose underneath the boiler).Open the taps slowly to let water enter the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close both taps tightly to stop the flow and check for any leaks.
Your boiler is struggling because there is trapped air or a blockage preventing water from circulating properly around your heating system.
Check your boiler's pressure gauge and top it up to 1.5 bar if it is below 1 barBleed all the radiators in your home starting from the lowest floor to the highestRestart the boiler once the system has been bled and repressurised
Your boiler has detected trapped air inside the system, which is causing the water temperature to rise much faster than it safely should.
Check your boiler pressure gauge to ensure it is between 1.0 and 1.5 bar.Bleed all radiators in your home starting from the lowest floor to the highest to remove trapped air.Re-pressurise the system to the correct level if the pressure dropped after bleeding the radiators.
Your boiler is failing to heat up because it cannot detect any water movement or temperature change, which usually indicates that your system pressure has dropped too low.
Check your boiler's pressure gauge on the front display; it should be between 1.0 and 1.5 bar.If the pressure is below 1.0 bar, locate the filling loop (usually a silver braided hose under the boiler).Open the valves on the filling loop to let water into the system until the gauge reaches 1.5 bar, then ensure the valves are fully closed.
on the Vaillant ecoTEC Plus 836
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 Vaillant 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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