Vaillant F72 Fault Code: What It Means and How to Fix It

Many boiler manufacturers incorporate fault codes in their boilers to alert homeowners to specific issues that prevent proper operation. Most of these error codes feature alphanumeric combinations to specify the type of problem to the homeowner, such as F7, F4, F9, or F72.

The Vaillant boilers also have fault codes, each having their potential solutions. Some problems can be resolved DIY, while others require a professional. The F72 Vaillant fault code is linked to faulty thermistors. It is fixable by replacing the thermistors or resetting the boiler. If the problem persists, contact a gas safe engineer.

So, let’s try to understand what this F72 Vaillant fault code means and whether it can be fixed via DIY or requires a professional’s help.

Essential Takeaways

• The F72 error code in Vaillant boilers is essentially due to faulty thermistors.
• Assessing and solving thermistor issues helps to keep your boiler efficient.
• Professional help is the best solution for getting rid of this problem permanently.
• Annual Boiler service is important to keep your boiler working correctly.

What Does F72 Mean on a Vaillant Boiler

If you have an F72 boiler fault, this means that there is an issue with the NTC thermistors inside your boiler. These are the flow and return NTC thermistors, namely. If this situation persists, then the thermistors will end up providing incorrect readings. If the flow and return thermistors show a significant difference for some time, then the boiler will turn off on its own and display the fault code F72.

Additionally, a Vaillant F72 can also be triggered if the boiler detects issues with either one of the NTC thermistors. This is because the NTC thermistors are in direct contact with your boiler’s PCB. Also, the NTC readings are required for boilers to accurately regulate their water temperature. Just like any other machine, boiler parts must all be in sync and in working condition for a properly working boiler.

Common Causes for an Inaccurate Reading with an NTC Thermistor

There are multiple reasons for this:

Defective Thermistor

This happens when one or both of your NTC thermistors are not working properly. It could also be that the return or flow thermistors were not installed correctly or might have declined in performance if you have an older boiler model.

Wiring Defect

It’s highly likely that an issue lies deep within the wiring in your NTC thermistors or the PCB. When it comes to wiring faults, it is highly suggested to contact a professional as they have prior experience in wiring management and/or detecting any persistent wiring issues.

Not Installed Correctly

This happens when the installer has not fitted the flow and return thermistors with accuracy. As compared to other reasons, this problem is least likely to occur as a professional installer will test that everything is functioning properly after installing your boiler.

Sludge and Debris Build-Up

A minimised flow rate in your boiler can cause inaccurate readings from the thermistors. When water isn’t flowing correctly, the sensors detect different temperatures. This triggers the F72 error code.

Magnetic Filter Issues

Magnetic filters capture metallic particles and sludge. If the filter is clogged, not maintained properly, then sludge moves freely. This further increases the flow problems and leads to inaccurate sensor measurements.

Effect on Heat Exchanger

Heat exchanger is an essential component for supplying heat affectively. Dirt and debris buildup in this component reduces rate of heat transfer and this ends up as the boiler triggering F72 fault code.

Clogged Radiators

Radiators play a major role in a balanced and smooth heat circulation. Improper balancing, airlocks or sludge buildup can cause the F72 fault code.

Incorrect Thermistor Readings from Circulation Problems

Because of the problems discussed above, reduced circulation causes thermistors to measure inaccurate temperature differences. These inaccurate measurements can affect the boiler’s control measurements and trigger its control system.

How to Prevent Circulation Problems

1. Radiators and Circulation Balance

Consistent radiator bleeding and balancing is essential for smooth circulation. This prevents inconsistent heating and minimises the chances of imprecise sensor readings.

2. Servicing Your Heat Exchanger

This requires a regular maintenance of your boiler which gets your heat exchanger timely serviced and free of any faults which can lead to F72 Vaillant error code.

3. Installing a Magnetic Filter

To prevent sludge buildup, you can install a magnetic filter. This ensures a clean boiler system and minimises the risk of circulation issues.

4. Utilising Inhibitors

Using chemical inhibitors is a great way to get rid of any corrosion problems and sludge formation. These chemical inhibitors not only extend the life of your Vaillant boiler but also decrease the likelihood of F72 fault code occurring.

Warning Signs of a Failing Thermistor

Boiler Shutdown

Before the central heating system is fully functional, the boiler might shut down multiple times. This is an indication of a faulty thermistor.

Unstable Temperature Regulation

When the boiler is supplying hot water, it might be excessively hot. This unstable temperature regulation indicates a thermistor fault.

Inconsistent Resistance Values

Contrast between the thermistor’s resistance values and the manufacturer’s mentioned range. If there’s a major contrast between the two, it could be the reason for an inefficient thermistor.

Diagnosing and detecting the F72 Error Code

There are multiple methods of finding and identifying the Vaillant boiler F72 fault code. As this Vaillant error code is due to faulty thermistors, the problem most likely is with this specific component or any other directly linked with it.

Ways to Test a Thermistor

• Visual Examination: Engineers inspect the thermistor for any physical damage.
• Resistance Measurement: Engineers often utilise a multimeter for determining the resistance of thermistors. This value should be according to the manufacturer’s specification. Once the temperature is raised, they check the resistance for any irregular signals.
• Checking the Wiring: Assess the wiring that is between the boiler’s control board and the thermistors. Make sure it is managed properly and is free from faults.

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How to Fix F72 Fault Code

Performing a Reset on Your Vaillant Boiler

One of the most basic solutions engineers perform is a thorough reset of your Vaillant boiler. For this, the boiler is switched off to allow it to cool down. Now restart the boiler and check if the boiler still shows the error.
If your boiler is new, a simple reset can sometimes clear the issue, but if the issue persists, you might need to consider the next steps.

Checking the Thermistors

Solving this issue requires a careful assessment of thermistors. Here, engineers check the resistance of the flow and return NTC thermistors. The wires of these thermistors are normally red and blue in colour. You might need to replace or get the thermistors serviced if the readings aren’t according to your boiler’s manual.

Solving Wiring Issues

Engineers solve any wiring problems between the circuit board of your boiler and the thermistors. Wiring problems include:

• Checking the cable bundles using a multimeter and make sure that there are no openings or breaks in these cables.
• Inspecting the X20 connector thoroughly, which is connected to the NTC wiring. Make sure that it’s not weary in condition and connected precisely.
• The NTC sensors must be linked to the pipes. The red wire must be connected to the heating flow NTC and the blue wire to the heating NTC.

So, you have a Vaillant boiler and are experiencing some common faults? Get more information about the fault codes you’re experiencing here:

• Vaillant F28 Fault Code
• Vaillant F29 Fault Code
• Vaillant F75 Fault Code
• Vaillant F22 Fault Code
• Vaillant F83 Fault Code

Timely Service to Prevent F72 Error Code

Conclusively, the best way to get rid of the F72 error code or any error code in your boiler is by getting it serviced in a timely manner. An annual service by a qualified Gas Safe engineer can solve any significant issues.

This means that the wiring, sensors, and thermistors are thoroughly checked to make sure they are working flawlessly. You can always contact a Gas Safe engineer if an unexpected F72 boiler fault occurs. You can also get a boiler cover, which is beneficial in unexpected boiler breakdowns.

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