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Vaillant Boiler Fault Codes

Your Vaillant boiler is one of the most technical appliances in your home. It is also one that you may take for granted until something goes wrong.

Luckily, boilers are clever enough to provide clues to the problem in the form of fault codes. Here we run through them all and what they mean.

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What does my Vaillant Boiler Fault Code mean?

Vaillant boilers can give us with a lot of information through their fault codes, helping professional engineers get a head start when undertaking a repair.

Fault code Fault

F.00 / F.0

Flow temperature sensor interruption or not connected

F.01 / F.1

Return temperature sensor interruption or not connected


Flow NTC short circuit or defective


Return NTC short circuit or defective


Safety switch-off temperature limiter - max temperature at the sensor is too high.


No/low water pressure


Safety switch-off temperature difference too great 


Safety switch-off temperature is rising too fast


Safety switch-off flue gas temperature too high


Error with gas valve – possible no function


Safety switch-off flame simulation


Failure during start-up – ignition unsuccessful to start


Failure during operation – re-ignition unsuccessful


Fan error - either defective or not connected


eBUS error – possible short circuit


Error with gas valve regulation


Error with gas valve – switch-off delay


EEPROM error


Electronics / NTC error


Electronic temperature error could be overheating due to external influences


Electronics flame signal error


Unstable flame signal error air in gas


Invalid device-specific number (DSN)


Flow NTC error – flow temperature sensor signal constant value


Flow return NTC error – temperature difference too great


Water pressure sensor signal in the wrong range, it is too low


Water pressure sensor signal outside correct range, the sensor signal is too high


Error with pressure – no pressure change detection when starting the pump


Overheating protection on – primary heat exchanger has responded


Flue non-return flap condensate pump error


Interruption to DHW outlet sensor at external controller


Flow and or return temperature sensor error


Error with flow/return temperature sensor temperature changing error


Error with flow and return temperature, sensor incorrectly fitted


No communication with the PCB (The PCB is what makes all electronic components in your boiler connect)

What is NTC?

An NTC or ‘Negative Temperature Coefficient’ is a type of thermistor (or thermal resistor).

Basically, it’s an electrical component that helps to regulate the temperature of your boiler. So, when you set your heating to a certain temperature it will make sure your boiler stays at that temperature.

Vaillant Boiler Safety Warning

When your Vaillant boiler error codes or fault lights flash, don’t do any repair work that involves working with gas as you are required to be Gas Safe Registered by law.

Here at Boiler Plan all our engineers are Gas Safe Registered and will do an amazing job with any Vaillant boiler repair work you may need.

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Protect your Vaillant Boiler with a Care Plan

There are a whole host of possible faults to be mindful of when it comes to your combi boiler. Which is why it’s best to be protected should anything unforeseen happen to your own heating system.

With our range of affordable care plans, there’ll be no need to fluster should you see a fault code.

Whatever plan you choose, each comes with an annual service to ensure your system is fully maintained and ready to keep your home reliably warm

Choose from:

  • Service PlanBoiler service every year to ensure it’s working correctly
  • Gold PackageIncludes: 3 call outs per year, annual service, carbon monoxide test.
  • Platinum PackageIncludes: Unlimited call outs, all parts and labour, repairs to the entire heating system, £500 towards a replacement boiler.
  • Boiler Plan Plus Package - For those with a Boiler still in warranty. Includes: Unlimited call outs, all parts and labour, repairs to the rest of your entire heating system.
Take out a care plan

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