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Last updated: 11th September, 2023


Vaillant F72 Error Code - How To Fix

Vaillant F72 Error Code - How To Fix

Key takeaways

  • The F72 error code in Vaillant boilers is typically related to problematic thermistors.
  • Identifying and fixing thermistor issues helps maintain boiler efficiency.
  • In some cases, professional assistance might be needed for a lasting solution.

If you're experiencing the Vaillant F72 error code on your boiler, our guide can help. We explain the common causes of the F72 error code and provide step-by-step instructions on how to fix it. We compare advice from reputable sources like Boiler Central, Heatable, and Easy Boilers to help you get your boiler up and running again.

Vaillant boilers are popular for their efficiency and reliability in providing hot water and central heating. However, like any appliance, issues may arise, such as the F72 error code.

Understanding what this code means and how to fix it is essential for homeowners to ensure their boiler runs efficiently.

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The F72 error code often indicates that there is a problem with the boiler's thermistors. These components are responsible for measuring the temperature of the water within the system, ensuring it remains consistent. Identifying common problems with thermistors and taking the necessary steps to fix them will keep your boiler functioning at its best.

In some instances, professional help may be required to assess the situation and implement a proper solution.

Understanding Vaillant F72 Error Code

Definition of F72 Error Code

The Vaillant F72 error code is a common fault found in Vaillant boilers, indicating an issue with the boiler's thermistors. These tiny but crucial components measure temperature changes within the central heating system, transmitting vital data to the boiler's control system. When the F72 fault code gets displayed, it implies that the boiler has detected an issue with either the flow or the return NTC thermistors, ultimately causing problems in heating performance.

Frequent Occurrence Reasons

There are several common reasons for the occurrence of the F72 Vaillant fault code:

  1. Faulty thermistors: The F72 error code often arises when the flow NTC thermistor and/or the return NTC thermistor are faulty, providing incorrect resistance readings. This can happen for various reasons, such as manufacturing defects or gradual degradation over time.

  2. Poor flow rate: In some cases, the fault code is triggered due to a poor flow rate through the boiler's main heat exchanger, which affects efficient heat distribution. This can result from debris build-up in the system, such as sludge or scale accumulation.

  3. Magnetic filter issues: If a magnetic filter is fitted on the return pipe, errors in filtering out any metal particles trapped within the system might cause blockages, subsequently leading to the F72 error code.

To address the issue, it is essential first to diagnose the cause behind the fault code accurately. A qualified heating engineer should inspect the boiler and carry out tests to determine whether the thermistors need to be replaced or if the problem lies elsewhere in the system. Once the root cause is identified and fixed, the Vaillant F72 error code should be cleared, allowing the boiler to operate efficiently again.

The Role of Thermistors in Vaillant Boilers

Function of NTC Thermistors

NTC thermistors are essential parts of Vaillant boilers. These tiny components play a crucial role in controlling and monitoring the heating water temperature. How do they work? To put it simply, the resistance of NTC thermistors changes in response to temperature fluctuations. A higher temperature in the water results in a decrease in resistance, allowing more electrical current to pass through, and vice versa.

Differentiating Between Flow and Return Thermistors

Flow and return thermistors are two types of NTC sensors found in Vaillant boilers. Both thermistors work as temperature sensors, but they are responsible for monitoring different aspects of water temperature. Flow thermistors detect the water temperature entering the boiler, whereas return thermistors gauge the temperature of water flowing back to the boiler after circulating through the heating system. These return pipe thermistors provide valuable information about the performance of the heating system, ensuring optimal function and energy efficiency.

Importance of Resistance Reading in Thermistors

In Vaillant boilers, resistance readings for both the flow and return NTC thermistors are crucial to maintaining optimal outputs and preventing issues like the F72 fault code. Engineers measure the resistance of NTC thermistors to assess their performance, as it indicates the water temperatures inside the system. Accurate evaluations allow early fault detection, which, in turn, helps prevent boiler shutdown or erratic water temperatures.

As we can see, NTC thermistors and their associated resistance readings are integral to the efficient and reliable operation of Vaillant boilers. By understanding their role and function, users can better comprehend the causes behind error codes such as F72 and seek appropriate solutions and repairs. Proper maintenance and understanding of thermistors ensure boiler longevity and optimal performance.

Identifying Common Problems with Vaillant Boilers

Symptoms of Defective Hardware

Defective hardware, particularly faulty thermistors, can cause the Vaillant F72 error code. When thermistors are not working properly, they can lead to issues such as the boiler shutting off repeatedly before the central heating or hot taps reach their full temperature. Additionally, the hot water may become too hot, or the boiler may keep shutting on and off. In such cases, replacing the defective thermistors could resolve the issue.

Wiring and Electrical Issues

Wiring and electrical problems can also contribute to the F72 error code. Damaged or faulty wiring, or issues with the wiring harness, can disrupt communication between the PCB and thermistors. Water damage is another potential cause of electrical issues in the boiler system. If an engineer identifies that the thermistors are not defective, they may need to address the wiring and electrical issues to fix the F72 error code.

Limescale Build-Up and Blockages

Limescale build-up and blockages can also cause problems within Vaillant boilers and potentially trigger the F72 error code. Limescale can accumulate within the boiler system over time, affecting the pump and other crucial components. This build-up can lead to blockages, impeding the proper functioning of the boiler and even causing issues with temperature control. To tackle this issue, a professional engineer may need to descale the boiler and remove any blockages present within the system. Such preventative maintenance can help ensure the boiler operates efficiently and without error codes like F72.

Testing and Detecting F72 Error

When it comes to the Vaillant F72 error code, there are various methods of testing and detecting the issue, particularly looking into faulty thermistors. In this section, we will discuss these methods and signs to help you diagnose and fix the F72 error.

Methods for Testing Thermistors

  1. Visual Inspection: First, examine the thermistors for any visible signs of damage or wear.

  2. Resistance Check: Use a multimeter to measure the resistance of the thermistors. This value should correspond with the manufacturer's specifications. As the temperature changes, observe the resistance for any intermittent signals.

  3. Continuity Test: Check the connections and wiring of the thermistors using a multimeter in continuity mode. Make sure there are no loose or damaged wires contributing to the F72 error.

  4. Evaluation of Wiring: Inspect the wiring between the thermistors and the boiler's control board, ensuring there is no damage or interference causing the error.

Signs of Faulty Thermistors

  • Boiler Shutdown: The boiler may shut down repeatedly before the central heating or hot taps reach the full heat. This could be a sign of a faulty thermistor.

  • Inaccurate Temperature Regulation: The hot water may be overly hot, or the boiler may shut down repeatedly. These are often signs of a thermistor malfunction.

  • Intermittent Signals: If, during testing, you notice erratic or intermittent signals, this could indicate a thermistor fault.

  • Divergence in Resistance Values: Compare the thermistor's resistance values with the manufacturer's specified range. If there's a significant discrepancy, it could signify a faulty thermistor.

In essence, detecting and fixing the Vaillant F72 error code involves testing the thermistors and examining for signs of faulty thermistors. By using the methods and monitoring the signs mentioned here, you can diagnose the issue more effectively and take the appropriate action.

Professional Help and Services

When to Call a Gas Safe Engineer

When dealing with a Vaillant F72 error, it is essential to recognise that although some issues can be resolved by the homeowner, there are instances when professional help is necessary. A Gas Safe Engineer should be contacted when issues such as faulty thermistors, wiring, or installation errors persist or become too complex to handle independently.


These engineers have the required skills and qualifications to correctly diagnose and repair your boiler, ensuring it operates safely and efficiently. They are registered with the official Gas Safe Register, providing you with the confidence that they are authorised to work on gas appliances.

As for the cost, this may vary depending on the complexity of the issue, the location, and the engineer's experience. It is advisable to obtain multiple quotes from different service providers to find the most competitive price. Keep in mind that opting for the cheapest option may not guarantee the best quality of work.

When it comes to plumbing services, a reliable plumber can be invaluable in maintaining your heating system in good condition. They can perform routine inspections and maintenance, which may help prevent future F72 error occurrences. However, ensure that they are also Gas Safe registered if they are working on your gas boiler.

In summary, knowing when to call a Gas Safe Engineer is vital for resolving your Vaillant F72 error code effectively. Consider the cost, qualifications, and experience of the professionals available to make an informed decision. Remember that safety and quality of work must always be prioritised.

Steps to Fix Vaillant F72 Error Code

Resetting the Vaillant Boiler

A simple solution to fixing the Vaillant F72 error code is often resetting the boiler. To do this, switch off the boiler and wait for a short period, allowing any residual heat to disperse. After a few minutes, turn the boiler back on and check whether the error has cleared. Sometimes, a reset might rectify the issue, but if the error persists, it may be necessary to take further steps.

Cleaning and Replacing Thermistors

In instances where the F72 error code arises due to faulty thermistors, it's crucial to address the issue as soon as possible. Start by checking the resistance of both the flow and return NTC thermistors - these typically have red and blue wires, respectively. If the resistance readings reveal an issue, you may need to clean or replace the thermistors.

  • Inspect the thermistors for any dirt or corrosion. If necessary, clean them carefully.

  • If cleaning does not resolve the issue or the thermistors appear visibly damaged, consider replacing them with new ones.

Handling Wiring and Circuit Issues

Wiring and circuit issues can play a significant role in the F72 error occurring on Vaillant boilers. Check the wiring between the thermistors and the PCB (circuit board) and ensure that all connections are secure. Look for any signs of deterioration or loose connections, which could lead to incorrect information being transmitted to the PCB.

To fix potential wiring problems:

  • Assess the wiring harness' integrity using a multimeter, ensuring there are no breaks or partial breaks in the cable.

  • Examine the X20 connector to which the NTC harness is linked, confirming that it's in good condition and properly connected.

  • Ensure that the NTC sensors are attached to the correct pipes; the blue wire should be connected to the heating return NTC, while the red wire should be linked to the heating flow NTC.

By following these steps, you can address the common causes behind the Vaillant F72 error code, ensuring that your boiler functions appropriately and efficiently.

Role of Radiators and Heat Exchangers

Understanding Importance of Heat Exchanger

A heat exchanger is a critical component within a Vaillant Ecotec boiler system, responsible for transferring heat from the burned gas to the water circulating within the system. The primary heat exchanger plays a vital role in heating the hot water that circulates through the radiators or underfloor heating, providing warmth to the living spaces. Its efficient functioning is essential to ensure the boiler system operates effectively, delivering the required heating and hot water to the household.

In an Ecotec boiler system, if the primary heat exchanger fails or experiences issues, the effect will be noticed promptly, potentially leading to poor heating performance and hot water supply. Consequently, it is of utmost importance to maintain the heat exchanger's optimal function to guarantee energy efficiency and comfort in the residential environment.

Checking the Radiators

Regularly checking and maintaining the radiators is a crucial aspect of ensuring optimal heating performance. Radiators serve as the primary method of distributing warmth throughout the living spaces, thus playing an indispensable role in a boiler system. Here are a few aspects to consider when checking radiators:

  • Bleeding: Air trapped in the radiators can prevent hot water from circulating effectively, causing inefficiencies and uneven heating. It is essential to bleed the radiators frequently to release trapped air and facilitate proper circulation.

  • Balancing: When some radiators emit more heat than others, it indicates an imbalanced system. By adjusting the radiator valves, the flow of water into each radiator can be regulated, ensuring uniform distribution of heat throughout the home.

  • Inspection: Regularly inspect the radiators for signs of wear, damage, or leaks, as these can compromise the heating system's efficiency. Promptly addressing any issues can minimise potential disruptions and maintain optimal performance.

In conclusion, the role of radiators and heat exchangers within a Vaillant Ecotec boiler system cannot be overstated. Ensuring their effective function and upkeep is essential to guarantee efficient heating and hot water provision, contributing to both energy savings and comfortable living spaces.

New Boiler Installation with iHeat

Identifying Need for New Boiler

Recognising when one needs a new boiler is crucial in heading off potential issues that could disrupt one's home. A Vaillant F72 error code typically indicates a boiler fault, which might involve faulty thermistors or several other problems. An F72 error code could cause the boiler to repeatedly switch off before the central heating or hot taps reach full temperature, or the hot water could end up being excessively hot.

In instances like these, it's essential to consider new boiler installation options. iHeat, a reputable service provider, would be instrumental in installing a Vaillant boiler, including models like the ecoTEC Pro, ecoTEC Plus and ecoTEC Exclusive. These boilers provide efficient heating and hot water supply, ensuring a warm, comfortable home.

When installing a new boiler, one would need to consider multiple factors to ensure a smooth process. The iHeat engineers will thoroughly assess the control panel and pipework to avoid any installation errors that could cause further issues. Proper attention to the workmanship can guarantee that the new system will not show signs of F72 or any other error codes in the near future.

In summary, identifying the need for a new boiler is essential for maintaining the comfort and efficiency of one's home. Trusting iHeat to install a Vaillant boiler can secure these benefits and eliminate error codes such as F72. By assessing control panels and pipework, iHeat engineers can ensure a seamless new boiler installation that will provide warmth and hot water for years to come.

Maintenance and Prevention Measures

Boilers are complex machines, and it's essential to maintain them properly to avoid errors like the Vaillant F72 fault code. This section will discuss two preventative measures that can help keep your boiler functioning efficiently: using a magnetic filter and inhibitor, and regular servicing.

Using Magnetic Filter and Inhibitor

A magnetic filter is an essential tool for preventing the buildup of sludge in your boiler. Sludge is made up of rust particles, dirt, and debris that can accumulate in the heating system and hinder its performance. By installing a magnetic filter on the return pipe of your boiler, you can effectively capture these particles and prevent them from causing damage.

In addition to the filter, using a chemical inhibitor is highly recommended. An inhibitor is a liquid that can be added to the central heating system to help protect it from corrosion, limescale, and sludge build-up. Using an inhibitor in conjunction with a magnetic filter can significantly prolong the life of your boiler and safeguard it against potential F72 fault codes.

Regular Services and Warranty Benefits

One of the most effective ways to prevent the occurrence of the F72 error code is by conducting regular boiler services. Annual service by a qualified engineer can detect any potential issues before they escalate or turn into expensive repairs. The engineer may check the sensors, thermistors, and wiring connections, ensuring that they are in good condition and functioning as intended.

Regular servicing can help ensure your boiler remains within the terms of its warranty. Many suppliers offer warranties on their boilers, and adhering to the service requirements can lead to significant savings in the event of a breakdown. It's essential to familiarise yourself with your boiler's warranty terms for ultimate peace of mind.

In conclusion, adopting maintenance and prevention measures like utilising a magnetic filter and inhibitor, along with regular servicing, can help keep your boiler in top shape. Adequate boiler care will also minimise the risk of encountering the Vaillant F72 fault code, ensuring your central heating system functions efficiently for years to come.

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Frequently Asked Questions

How do I reset my Vaillant F72 boiler?

To reset your Vaillant F72 boiler, locate the reset button on your boiler's main panel. Press and hold the button for a few seconds, then release it. The boiler should initiate its reset process, which may take some time. Once complete, check if the F72 error code has been resolved. If the issue persists, contact a Gas Safe registered engineer for assistance.

What does F72 mean on a Vaillant boiler?

F72 error code on a Vaillant boiler indicates a difference in temperature between the flow and return thermistors, which likely results from a defective NTC (Negative Temperature Coefficient) thermistor, or wiring issues. The thermistor regulates the water temperature in the heating system, and a faulty one can cause unstable boiler operation.

What is the fault 72 on a Vaillant Ecotec Plus 430?

Fault 72 on a Vaillant Ecotec Plus 430 is the same as the F72 error code. It typically signifies a temperature differential issue caused by either defective thermistors or a problem with their wiring. Engaging a qualified engineer will help assess and rectify the issue accordingly.

What does F72 mean on a Glow Worm boiler?

The F72 error code is specific to Vaillant boilers, while Glow Worm boilers may have different error codes for similar issues. Consult your Glow Worm boiler's user manual or contact a Gas Safe registered engineer to identify and address the specific error code in your boiler.

How do you fix a flow thermistor fault?

To fix a flow thermistor fault, follow these steps:
1. Turn off the boiler and isolate it from the mains.
2. Verify both flow and return thermistors are functioning correctly.
3. Inspect the wiring for damage or loose connections.
4. Replace any defective thermistors.
5. If you're not experienced in boiler repair, it's best to enlist the help of a Gas Safe registered engineer to diagnose and fix the issue.

How do I know if my thermistor is broken?

A broken thermistor often results in inaccurate temperature readings and unstable boiler operation. Some signs of a faulty thermistor include:
- Fluctuating water temperature
- Boiler cycling on and off frequently
- Error codes related to temperature regulation or differential
To confirm if your thermistor is indeed broken, a Gas Safe registered engineer can perform a temperature resistance test and evaluate the boiler's overall performance.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.