24/7 call-out service

Have a question?

Vaillant Boiler F64 Fault Code

The Vaillant fault code F64 boiler electrical problem Q & A or require an engineer for an emergency boiler repair.


The Vaillant Boiler Fault Code F64 Error Common Q&A

Vaillant Boiler F64 Fault Code

Vaillant Boiler F64 Fault Code Error
  • What does the F64 fault code mean on my Vaillant boiler?
  • What are the symptoms of failed electrical connections?
  • Can the F64 fault be fixed by resetting my Vaillant boiler?
  • What are boiler NTC thermistors?
  • How can the NTC thermistors fail?
  • Why does electrical wiring fail on temperature sensors?
  • Can a faulty NTC thermistor be fixed?
  • My engineer says it’s the thermocouple that needs replacing, what’s that?
  • How will water make its way into boiler connections and cause damage?
  • QHow do I stop electronic components getting damaged by leaks?
  • What is scale?
  • How can limescale cause a F64 and NTC thermistor fault?
  • What are common signs of limescale build up around the NTC thermistor?
  • How can limescale build-up be removed to fix the F64 fault?
  • How will the engineer know if the PCB is causing the F64 fault code?

What does the F64 fault code mean on my Vaillant boiler

According to Vaillant, the F64 fault code is an electrical error.

The error can be pinpointed to:

  • NTC thermistors on the flow and return boiler pipes
  • Faulty connections
  • PCB fault

What are the symptoms of failed electrical connections

Electrical faults can easily be confused with other faults on boilers.

A boiler’s display panel will always display the most relevant fault code it can find, but that doesn’t mean it explains the fault fully.

Typically, a boiler with weak or loose connections, a faulty thermistor or broken PCB will:

  • Work intermittently – the boiler will cycle on and off
  • Won’t get up to temperature
  • Will lock out regularly and need resetting

Can the F64 fault be fixed by resetting my Vaillant boiler

First, the diagnostic and replacement of boiler parts is a job for a Gas Safe engineer.

Call one in, and let them fix the issue, and they’ll reset your boiler when it’s safe to do so.

Boilers lockout and display fault codes as there’s a potential safety issue. So, they shouldn’t be reset until the fault has been fixed.

Secondly, simply resetting boilers can clear a fault for a few minutes.

But, that’s at the risk of safety, the problem will re-emerge, and the boiler will lock out again.

What are boiler NTC thermistors

NTC thermistors are electronic components.

Some NTC thermistors will be “wet”. That means, they’ll be in the central heating pipework, and they’ll monitor the water temperature.

Other NTC thermistors are dry. Dry thermistors will be located on (rather than in) the flow and return pipes, and measure the temperature of the pipework.

These electronic components don’t give off readings in temperature, but in electrical resistance.

As heat rises, the resistance given off will decrease. On the flip-side, when temperature decreases, the resistance increases.

These signals are communicated back to the boiler’s PCB (the circuit board that controls the boiler).

And, the boiler knows whether to increase or decrease temperature by supplying more/cutting off gas.

How can the NTC thermistors fail

Like any boiler and central heating parts, NTC thermistors can fail.

They can give off readings that are intermittent, due to electrical issues.

Usually, this will be caused because of:

  • Electrical errors within the NTC thermistor itself (the thermistor is faulty)
  • A wiring fault to or from the sensor (loose or damaged connections)
  • A wiring fault to or from the PCB
  • The PCB being faulty

Why does electrical wiring fail on temperature sensors

This could be for many reasons:

  • Poor wiring from the manufacturer
  • Wiring that has degraded over time
  • Worked loose by vibrations from the flow and return pipes
  • Water has made its way into connections
  • Scale build-up on terminals, or near to the NTC sensor

Whatever the cause of the problem, the wiring will need to be either repaired or replaced.

Otherwise, the boiler will continue to react intermittently.

Can a faulty NTC thermistor be fixed?

NTC thermistors in boiler terms, are cheap parts. The cost really relates to labour for diagnosing the problem and fitting the parts.

It will take a similar amount of time to diagnose and fix the NTC thermistor (including checking wiring), as it would to replace the sensor.

So, it makes sense to have a new unit fitted, rather than reconditioning the old one.

My engineer says it’s the thermocouple that needs replacing, what’s that

Thermocouples and thermistors are similar, but not the same.

They are both temperature sensors, although they have different operational conditions.

How will water make its way into boiler connections and cause damage

Leaking boilers are a big problem.

Typically, the water will come from cracked heat exchangers, and leaking pumps.

When this is the case two things will happen:

  • The water will drip onto components
  • The water will be heated by internal boiler components (in normal operation), and condensation will settle on electronic components and connections

How do I stop electronic components getting damaged by leaks

First, the leak needs to be identified by a boiler engineer.

The culprit needs to be either fixed (for instance, seals in the pump replaced), or completely replaced (for instance, a cracked heat exchanger).

Once the leak has been sealed, the electrical components will need to be repaired, or replaced.

Unfortunately, water can cause lasting damage so depending on the parts (i.e. PCB) that have been damaged, they might have to be replaced to prevent further problems with your Vaillant boiler.

What is scale

Scale, is limescale. It comes from mineral deposits in water that flow around your central heating system.

It can cause a whole host of heating problems including:

  • Radiators not getting hot
  • The return pipe is cold, even when the flow pipe is hot
  • Cracked heat exchangers
  • Noisy heating pumps

If you reside in a hard water area, the chances of scale deposits being left in your heating system are higher, compared with those in softer water areas.

The limescale attaches itself to the heating system (pipes, boiler components etc)

How can limescale cause a F64 and NTC thermistor fault

Limescale is notorious for creating hotspots. Where it attaches itself, the pipework or individual boiler component will burn hotter.

In fact, this is the exact issue that can cause heat exchangers to crack. The increased temperature on a small section of the heat exchanger creates a weak spot, and it eventually cracks.

Although NTC thermistors are not going to crack, they do monitor temperature.

So, when limescale attaches itself near or onto the thermistor, it will burn hotter, and give an inconsistent temperature reading.

The area around the NTC thermistor will show a temperature that is much hotter than the actual temperature of the water.

Due to this higher temperature, the NTC communicates with the PCB to tell it water is too hot (or, its hot enough), and the PCB translates that into “no need for more gas or heat”.

Conent

What are common signs of limescale build up around the NTC thermistor

Firstly, when there are big sections of limescale build-up, it’s likely you’ll get kettling in the pipes.

They’ll start to make small sounds (that almost sound like whistling and popping; similar to a kettle).

This will be small steam bubbles popping, and a sign of a section of pipework overheating.

Secondly, it’s likely your boiler will constantly turn off before radiators are up to temperature. As mentioned, the boiler thinks it’s up to temperature; that’s why it’s turning off.

This translates into a colder than usual return pipe.

And, if the difference between the flow and return pipe temperature is too low, the boiler will lockout and show another fault code.

How can limescale build-up be removed to fix the F64 fault

Luckily, the thermistor is most likely where the limescale has built-up, not the pipes. Replacing the thermistor will fix the problem, rather than cutting out and replacing sections of copper pipe.

But, without preventative measures in place, the issue will return.

If limescale has become this much of a problem, it’s likely your heating system would benefit from a hot flush, or power flush.

Powerful cleaning chemicals will then attack limescale and dirt in your system, and then be flushed out.

A longer-term preventative measure comes in the form of central heating inhibitor, and a scale reducer.

The inhibitor will help to break down the scale into tiny pieces. This gets the scale to a small enough size so when they pass through the scale reducer, they’re caught.

The limescale will then build-up in the filter (ready to be cleaned, with your next boiler service), rather than settling on components that control your heating system, like the NTC thermistors.

How will the engineer know if the PCB is causing the F64 fault code

A series of electrical tests will help determine the PCB is at fault.

It’s useful to explain any faults you’ve noticed, and pass this information on to the engineer (as these faults might be intermittent, and not visible when the engineer arrives).

This may help speed up the diagnostic process.

This might include:

  • The display panel flickering, or working intermittently
  • The boiler turning on and off randomly, or before radiators are up to temperature
  • Noises coming from pipework, or from within the boiler
  • Any boiler leaks, as well as the amount of pressure that the boiler loses over days/weeks

After these electrical tests, the engineer will be able to determine if it’s the PCB that needs replacing, or a cheaper part.

Other Vaillant Fault Codes And Error

If your looking for the list of error codes relating to the Vaillant boiler then please read the article Vaillant Boiler Fault Codes And Cures