Vokera A08 fault code on boiler

This fault will appear on the Vokera boiler display screen. You will need to fix the following internal problems before you can get your central heating system back up and running.

Because the diagnosis and repair for the A08 fault will require the removal of the boiler’s cover it is legally required that a registered Gas Safe engineer do so.

The costs and time required to correct this fault and get your heating and hot water working again can vary greatly. This guide will help you understand the possible causes and what to do about them.

What does the Vokera Boiler’s A08 Fault mean?

Vokera says the A08 fault code means one of the following:

  • Return NTC thermistor fault
  • NTC return thermistor temperature
  • Temperature differential inverted

This is one of the more expensive Vokera boiler fault codes

What’s a Return NTC Thermistor, you ask?

A thermistor, a small component of an electrical circuit that changes resistance when water passes through it, and are small electronic heating temperature sensors. These changes travel along a circuit to the printed circuit board (PCB), where they are used to measure the temperature in the system.

This is why the name “thermistor” was created. It combines “thermal” with “resistor”. NTC is the Negative Temperature coefficient. This means that the resistance of the thermistor decreases as the temperature rises around it.

Two of these tiny electrical components are located in your boiler. However, this fault is only for the one on the return pipe.

This is the pipe that allows water to re-enter the unit after it has passed through the heating system. It is not the flow pipe that heats the water.

The thermistor measures the temperature of the water as it flows back into the unit.

The Vokera boiler will display an A08 fault code if it gets a signal that the water temperature is too high or too low.

What Causes a Return NTC Thermistor Failure on a Vokera boiler?

This fault could be caused by incorrect installation. The thermistor and any relevant connections were not properly connected causing your heating and hot water not to work properly

If you recently had your Vokera boiler replaced or if there was a specific job that required the thermistor to be repaired, this is a possible option.

Even with older systems, wiring and connections to thermistors may be loose. Vibrations from components like the pump can cause vibrations in the unit.

These vibrations are not always a sign of a bigger problem. Boilers generally vibrate more as they age.

You may have more than one problem with your thermistor if you hear unusually loud heating sounds.

Sometimes, the electrical faults can cause thermometers to stop working entirely or produce incorrect readings. As parts age, these faults become more common.

How can a Gas Safe engineer fix a faulty Vokera return NTC thermistor?

Before replacing the thermistor, your engineer will first need to determine if the thermistor has failed.

A multimeter is a tool that measures resistance. This will enable them to check if the thermistor is responding accurately to the water surrounding it.

They will be able to identify any loose connections if they are not obvious in a visual inspection.

It is usually quite simple to fix loose connections and get things hooked up again. It is necessary to replace the thermistor if it is not working correctly or at all.

These parts are usually cheap and rarely cost more than £20. The main cost of this repair will be the labour time.

Can a faulty pump cause Vokera A08 Fault code?

The PCB can be used to ensure that both the return and flow thermistors work as they should.

The PCB will detect if one of the pipes is unusually hot or cold and register this, causing it to lock out.

If the reading is not correct, the thermistors may be faulty. However, if it is accurate, then there is likely to be a circulation problem.

The main component that circulates heated water from the boiler to the heating system is the pump.

It can cause inconsistent circulation if it becomes blocked or faulty.

If water volume exceeds the return thermistor’s limit, it can affect its resistance reading, which causes the PCB to register an increase in temperature.

Pump blockages are most commonly caused by heating sludge and air locks.

When the pump is being vacated, air can enter the pump. Heating sludge can be described as a mixture of tiny pieces of rust and debris that melt into water pipes to form sludge.

The debris moves slowly through the system and can eventually cause a blockage or blockage to a pipe or part like the pump.

Pump failure is more common in older boilers because the moving parts that enable it to spin are worn down causing issues with your heating and hot water pressure.

These are also known as shaft and bearings. As the bearings wear down, the pump will stop rotating freely.

There is a possibility that your new boiler or pump was installed recently.

How can Gas Safe engineer fix a faulty pump?

Your engineer can reset the pump if it has been set incorrectly. If your boiler was installed recently, this is unlikely to happen. It’s worth calling the person who installed it as they will know the setup.

The “bleed screw” allows air to escape from the pump’s airlocks before they can be reinstalled.

Heating sludge blocks can be more costly and time-consuming to fix, but they are important to do right as they can lead to further damage.

An engineer may perform a procedure called a flush. This involves sending chemicals along with water through the entire heating system to dissolve any blockages.

This will depend on how many radiators you have in your home. The base cost is usually between £300-£400, and then goes up to £100 per radiator.

A magnetic filter, which captures any debris, can be installed to prevent blockages in the future. They are usually less than 100 pesos and are worth the investment for future repairs. Each boiler service can be completed by cleaning the filter.

It may be possible to repair the parts of the pump, but it is likely that your engineer will recommend a complete replacement.

Pumps that fail will continue to fail until they are replaced. Modern pumps can be as high as £300 but prices can vary depending on the model.

Is a Faulty Printed Circuit Board (PCB) a Cause of the Vokera-A08 Fault?

After examining all possible causes, your engineer may suggest that the PCB is the problem, causing it not to read the thermistor signals correctly.

The whole boiler depends on the PCB for its functionality. If the multimeter finds a fault, the part will need to replaced. They can run up to £500.

What does Temperature Differential inverted mean?

This fault is rare and only occurs in very new installations. This means that the temperature reading expected from the return thermometer has been derived from the flow thermometer, and vice versa.

As the heat exchanger warms water, it should measure flow at a higher level.

This could be caused by incorrectly installing the pump. It may circulate water in the wrong direction or flow and return thermistors within the wrong pipes.

These issues will cause the heating system to stop working long-term, so they need to be addressed soon after installation.

How can I reset my Vokera Boiler after the A08 Fault?

It is unlikely that you can fix your boiler’s fault codes. They are only displayed when there is an underlying problem.

You can, however, safely reset your boiler without calling an engineer.

Even if this works, it is worth calling someone to report the fault codes. It may not last, and this will keep a record of any issues that could be used to aid in future repairs.

Does the A08 Fault mean That My Vokera Boiler is Dangerous?

Your boiler will not be at risk of causing external danger if the A08 fault is detected.

It has already been locked out to protect against such danger so forcing it to stop is not an option and altering the system water pressure is not a good idea.

To prevent overheating and other problems, the boiler must accurately measure temperature. This will ensure that the Vokera boiler is ok to operate safely.

Does the Vokera A08 Error codes mean I need a new boiler?

If your Vokera boiler has a thermistor fault, then it is likely going to cost you a few hundred pounds at least. Usually it is that start of more fault codes so it may be more economical in the long term to get a new boiler, especially if your Vokera boiler issues start to keep happening.

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