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Last updated: 28th January, 2024


Vaillant F83 Error Code

Vaillant F83 Error Code

Key takeaways

  • The F83 fault code in Vaillant boilers signifies a malfunction related to the return temperature sensor.
  • Homeowners can perform rudimentary checks, but technical resolution typically requires Gas Safe registered professional expertise.
  • Immediate inspection by a certified engineer is recommended to address the fault efficiently and safely.

Boiler error codes are essential indicators assisting in the diagnostics of potential issues within a boiler system. They operate as a shorthand, allowing homeowners and engineers to quickly identify and address problems.

Vaillant boilers, well-regarded for their efficiency and reliability, are not immune to issues, one of which is signalled by the F83 fault code. 

This particular error is indicative of a fault within the boiler's internal workings, specifically relating to the return temperature sensor. The occurrence of this fault code suggests that the sensor has detected an insufficient rise in temperature shortly after the boiler has fired up.

Seeing the F83 error on your boiler's display can be a cause for concern, as it usually implies a disruption in normal operation, requiring prompt attention. While some basic troubleshooting steps can be performed by the homeowner, such as checking the pressure levels and bleeding radiators, the technical aspects of resolving this error often necessitate professional intervention. 

It is a safety precaution as well as a compliance requirement to have a Gas Safe registered engineer diagnose and remedy the problem, ensuring that the repair is conducted according to the stringent standards set for gas appliances.

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What Is a Boiler Error Code?

Boiler error codes are essential indicators assisting in the diagnostics of potential issues within a boiler system. They operate as a shorthand, allowing homeowners and engineers to quickly identify and address problems.

Explain What Boiler Error Codes Are in General

Error codes appear on a boiler's display panel or interface when the system's internal diagnostics detect a malfunction or irregularity. Typically, these codes consist of letters, numbers, or a combination of both, pinpointing the exact nature of the issue at hand. The display of an error code often triggers as a result of:

  • Deviations in expected operational parameters (e.g., temperature, pressure)

  • Component failures (e.g., valves, sensors, pumps)

  • Communication breakdowns between boiler parts

  • Necessity for routine maintenance or recalibration

Understanding these codes can drastically streamline the troubleshooting process, allowing for a more efficient boiler repair and service workflow.

Importance of Understanding Error Codes for Boiler Maintenance

The significance of comprehending boiler error codes cannot be overstated. Accurate interpretation guides homeowners in:

  • Identifying if the boiler requires immediate attention

  • Determining the severity of the fault

  • Deciding whether professional assistance is needed for complex repairs

For maintenance engineers, a firm grasp of these codes facilitates a logical, methodical approach to boiler service, ensuring all components are functioning correctly. Regular boiler servicing can preempt the emergence of fault codes, signalling the importance of preventative care. Moreover, understanding these codes helps avoid unnecessary expenditures by resolving simple issues that do not require professional intervention.

What Does the Vaillant F83 Error Code Mean?

The Vaillant F83 error code is an indication of a temperature discrepancy in the boiler operation, signalling an issue with the system’s temperature sensing mechanism.

Detailed Description of the Specific Error Code

The error relates to the return temperature sensor that is attached to Vaillant boilers. This sensor is responsible for monitoring temperature variations. When the burner is activated, and the sensor detects an insufficient temperature rise, the F83 fault code is presented. It focuses on the difference between the temperatures of the water entering and leaving the boiler through the flow and return pipes. These temperature readings are critical in managing the efficiency and safety of the heating system.

Possible Reasons Why This Error Code Appears

There are several potential causes for the F83 fault code to surface:

  • Thermistors malfunction: Vaillant boilers utilise NTC thermistors (Negative Temperature Coefficient thermistors) to gauge water temperature. If these sensors, particularly the return temperature sensor, malfunction, they may send incorrect readings that trigger the F83 code.

  • Leaks in the System: Any leak within the heat exchanger or other parts may cause pressure drops and imbalanced temperatures.

  • Pressure Issues: An irregular reading on the pressure gauge can signify a problem with the water pressure that directly affects temperature consistency.

  • Faulty Gas Valve: An improperly working gas valve may fail to regulate the flow of gas correctly, influencing the boiler's ability to heat water to the required temperatures.

  • Heat Exchanger Complications: A blockage or damage in the heat exchanger can prevent the boiler from warming the water effectively, resulting in insufficient temperature rises.

Understanding these specific causes can assist a user or technician in approaching the F83 error code with a tailored solution, enhancing the likelihood of a precise and efficient fix.

Signs of the Vaillant F83 Error Code

When a Vaillant boiler encounters an F83 error code, this indicates specific issues with the system's internal operation. Key signs accompanying this error code include:

  • Low Boiler Pressure: If the pressure gauge on your boiler indicates a drop below the standard operating range, typically below 1 bar, it points to low water pressure. This is a common culprit for the F83 error code.

Boiler Status

Pressure Reading

Potential Action Required

Normal Operation

~1.5 Bar

Monitor as usual

F83 Error Displayed

Below 1 Bar

Re-pressurise or investigate leaks

  • Temperature Fluctuations: The boiler will detect incorrect temperature changes between the flow and return pipes. An effectual disparity in these readings can trigger the F83 fault.

    • Flow Temperature: The water temperature as it leaves the boiler should be consistent.

    • Return Temperature: The water returning should not be overly cool compared to the flow temperature.

Incorrect temperature readings suggest problems with the boiler's thermistors, which are responsible for measuring water temperature. If said thermistors are poorly calibrated or experience wiring faults, they may supply incorrect temperature data, thus setting off the F83 error.

In instances where the boiler shows the F83 code, it will likely undergo an automatic safety shutdown to prevent further damage. Professional assessment by a Gas Safe Engineer is typically advised to determine the precise cause and administer the appropriate fix. It's important to address these signs promptly to ensure the boiler operates efficiently and safely.

Can I Fix This Boiler Error Code Myself?

When a Vaillant boiler displays the F83 fault code, it signals issues with temperature variations in the heating system. Homeowners may approach certain steps to address this fault, though caution is advised.

DIY Tips for Resolving the Error

Certain aspects of the F83 error can be tackled with a do-it-yourself approach. Here's what you can try:

  • Repressurise the Boiler: Check the boiler's pressure gauge; if it's below 1.0 bar, the system requires repressurising to between 1.0 and 1.5 bar.

  • Bleed Radiators: Air trapped in the central heating system can cause uneven heating and pressure imbalances, bleeding the radiators may remove this air.

  • Check for Loose Connections: Inspect electrical connections to ensure they're secure, as faulty wiring can lead to erroneous fault codes.

Warnings or Advice on When to Avoid DIY and Seek Professional Help

Despite the allure of tackling boiler issues independently, certain situations necessitate professional intervention:

  • Low Boiler Pressure Persisting: If repressurising the boiler doesn't remedy the pressure issue, the system could harbour leaks or have a defective pressure relief valve.

  • Suspected Faulty Wiring: Should you suspect wiring issues beyond loose connections, it's time to cease the DIY route. This is a matter for a certified engineer, as faulty wiring can pose significant risks.

  • Comprehensive Error Diagnosis: The F83 fault can stem from intricate components such as thermistors. If resetting and basic troubleshooting don't clear the error, a Gas Safe registered professional should assess the boiler.

Do I Need to Contact a Gas Safe Engineer to Fix This Error Code?

Encountering an F83 error code on a Vaillant boiler signifies a specific issue that often requires professional intervention. This section breaks down the circumstances that necessitate calling in a Gas Safe Registered Engineer and underscores the importance of their role in boiler repairs.

Advice on When It's Necessary to Call a Professional

An F83 error code on a Vaillant boiler indicates a faulty temperature difference between the flow and return pipes, usually after the boiler has fired up. Simple situations, such as repressurising your boiler or hitting the reset button, can sometimes be resolved without expert help. However, this code often points to more intricate problems, including:

  • Faulty temperature sensors or their incorrect placement.

  • Malfunctioning pumps.

  • Issues requiring parts replacement.

In such cases, engaging a Gas Safe Registered Engineer is not just recommended, but essential for safety and compliance with legal standards.

Explanation of What a Gas Safe Engineer Is and Why Their Expertise Is Important

The Gas Safe Register is the official list of gas engineers who are legally allowed to work on gas appliances in the UK. These engineers undergo rigorous training and assessment to ensure they comply with the latest safety standards.

When encountering an F83 error:

  • The expertise of a Gas Safe Engineer is critical to diagnose and fix complex boiler issues safely.

  • Their qualifications enable them to handle potentially dangerous repairs, ensuring that your heating system is not only functional but also safe to use.

  • They can expertly determine whether the problem lies with thermistors, wiring, or any other component, and they can source and install genuine parts where necessary.

In short, for any non-trivial issue linked to the F83 fault code, professional assistance from a Gas Safe Registered Engineer is more than just a recommendation—it's a requisite to ensure the continued safety and efficiency of your home heating system.

How Much Does Fixing the Vaillant F83 Error Code Cost?

When the Vaillant F83 error code flashes on the boiler's display, it indicates a fault that commonly involves the heat exchanger or temperature sensors. Correcting this fault requires a variable cost, depending on several factors.

General Cost Range for Fixing This Error

Costs for fixing an F83 error can vary widely. Broadly, one may face charges ranging from £100 to over £500. This estimate includes call-out fees for a Gas Safe registered engineer who will diagnose the issue and, if necessary, execute the repair.

  • Boiler Service: £70 - £150

  • Parts Replacement: £100 - £400 (part dependent)

  • Labour: £40 - £150 per hour

Factors That Might Affect the Cost

Several aspects can dictate the final cost of repairing an F83 error:

  • Type of Fault: A simple repressurising may come in cheaper, while a faulty heat exchanger could lead to the higher end of the cost spectrum.

  • Parts Replacement: The need for new parts, such as temperature sensors or a heat exchanger, can increase expenses. For instance:

    • Temperature Sensor: around £50-£100

    • Heat Exchanger: upwards of £300

  • Engineer's Expertise: Highly experienced professionals might charge more for their service.

  • Region: Labour costs can fluctuate by region; urban areas often see higher rates.

  • Boiler Age and Warranty: If the boiler is aged or out of warranty, it might lead to additional costs for parts that are not covered.

Each repair presents its unique challenges, and conversely, for some fortunate individuals, the repair may be relatively straightforward and cost-effective. A detailed diagnosis by a qualified technician can provide homeowners with a more precise quotation.

Do I Need a New Boiler?

Encountering a Vaillant F83 error code can be daunting, but it doesn't immediately signal the need for a boiler replacement. Careful consideration is required to assess whether a repair will resolve the issue or if investing in a new boiler is more prudent.

Criteria to Decide Whether a Repair Is Sufficient or If a New Boiler Is Required

Several factors come into play when deciding between repairing a boiler and purchasing a new one. The severity and source of the F83 fault, which is often linked to sensor malfunction or internal leakage, must be accurately diagnosed by a qualified engineer. For Vaillant ecoTEC plus models, minor part replacements or sensor issues typically favour repairs over a replacement.

  1. Age of Boiler: Boilers over 10 years old may be less efficient and more prone to frequent breakdowns.

  2. Frequency of Breakdowns: Regular malfunctions may indicate that a boiler is nearing the end of its operational life.

  3. Cost of Repairs: If repair costs are substantial, nearing a large percentage of a new boiler price, replacement might be more cost-effective.

  4. Efficiency Levels: Modern boilers are more energy-efficient. Consider upgrading if the current boiler efficiency is below standard.

Information on the Lifespan of Boilers and When Replacement Is Typically Recommended

Boilers have an average lifespan of around 10-15 years. It's typically recommended to consider replacement in the following situations:

  • When a boiler reaches the 10-year mark and major components fail.

  • Efficiency has significantly deteriorated, particularly in models predating the central heating systems' condensing technology.

  • Current boiler no longer meeting the household heat and hot water demands effectively.

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Boiler costs can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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System to system


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In addressing an F83 fault code on a Vaillant boiler, it is essential to understand the underlying issues. This code signifies an abnormal temperature variance between the flow and return pipes, typically indicating a failure in the thermistors or the electrical connections. Thermistors are vital in monitoring the water temperature at different stages of the heating process. Correct function ensures that central heating systems, including radiators and towel rails, distribute heat efficiently.

Substantive maintenance is paramount, including an annual boiler service, which might prevent such faults. These services can identify if the boiler pressure is optimally maintained, which is integral to a fully functioning central heating system. Inaccuracies here could lead to the manifestation of fault codes.

Users with thermostats that are not calibrated correctly might also encounter this F83 code. Thermostats interact directly with the boiler to regulate the temperature across the system. If they send incorrect signals, the boiler could register this as a fault. Thus, it is crucial to ensure thermostats are functioning correctly to avoid false alarms.

If a user faces this fault, they should consider engaging qualified professionals who possess the expertise to diagnose and resolve such issues. It's recommended to seek assistance rather than attempt unguided troubleshooting, as this could exacerbate boiler issues or negate manufacturer warranties. Most importantly, safety must remain the overarching priority when dealing with complex boiler systems.

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Frequently Asked Questions

How do I fix the fault on my F83 Vaillant boiler?

Should your Vaillant boiler display an F83 error, this typically indicates a problem with the system's water circulation, often due to incorrect temperature changes. First, check for any signs of leaks or blockages. If the problem persists, a professional engineer may need to examine the thermistors and possibly replace them.

What is the code F38 on a Vaillant boiler?

The F38 error signifies a low water pressure issue in your Vaillant boiler. You can attempt to resolve this by repressurising your boiler system. Check the manufacturer's manual for specific instructions on how to repressurise your model.

What is code F 73 Vaillant?

Code F73 indicates a water pressure sensor differential. This could reflect a water circulation problem, typically due to air within the system or a faulty water pressure sensor. It is advisable to call a registered engineer to diagnose and remedy the issue.

What does F83 mean on a Glow Worm boiler?

On a Glow Worm boiler, the F83 code also points to water circulation problems. This may include issues such as pump failure or blockages in the system. Professional assessment is recommended to determine the exact cause and implement repairs.

How do I clear my Vaillant fault code?

To clear a fault code on a Vaillant boiler, reset the boiler using the designated reset button or turning it off and then on at the mains supply. If the fault reoccurs, further investigation by a certified engineer is necessary.

Should I turn my boiler off if it has a fault code?

If your Vaillant boiler displays a fault code, it is generally safe to leave it on until an engineer checks it. However, if you notice any signs of a gas leak or if the boiler is making unusual noises, turn it off immediately and contact a professional.

Are Glow Worm and Vaillant boilers the same?

Glow Worm and Vaillant boilers are part of the same group, with Vaillant being the parent company. Both brands share some technologies, but they have their own range of products and may display different fault codes.

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