The F75 fault is one of the most commonly encountered issues in Vaillant and Glow-worm boilers. It frustrates many homeowners, especially during the colder months when reliable heating is crucial. This error code typically points to problems with the boiler’s pressure sensor or pump. Understanding why this fault occurs and how to fix it can save you time, stress, and the inconvenience of a broken heating system.
What Does the F75 Fault Mean?
When your Vaillant or Glow-worm boiler displays an F75 error, it cannot detect a rise in water pressure after the pump starts. In a healthy system, the pump circulates water, and the pressure sensor monitors the system to ensure that pressure increases accordingly. If this pressure increase isn’t detected, the F75 code is triggered, and the boiler shuts down to prevent potential damage.
Why Do Vaillant and Glow-worm Boilers Suffer from F75 Faults?
There are several reasons why the F75 fault may occur, and it’s a common issue, particularly in older models of these boilers. Let’s explore the most common causes:
- Faulty or Blocked Pressure Sensor
The pressure sensor is a critical component that monitors changes in water pressure. Over time, the sensor can become faulty, especially in older boilers, leading to inaccurate pressure readings.
Blockages are another frequent culprit. Sludge, limescale, or debris can accumulate inside the sensor, particularly in systems that haven’t been flushed or maintained regularly. This blockage prevents the sensor from accurately detecting pressure changes, triggering the F75 fault.
- Pump Issues
The pump circulates water throughout your heating system. If the pump isn’t working properly, your boiler won’t detect the necessary pressure rise, causing the F75 error.
Worn-out Pump: As the pump ages, it can weaken or fail altogether, reducing its ability to circulate water efficiently.
Air in the System: Air trapped in the boiler system can impede the pump’s operation, reducing water circulation and pressure issues.
Sludge and Blockages: Over time, central heating systems accumulate sludge, particularly in areas with hard water. These blockages increase resistance, making it harder for the pump to work, which in turn causes the pressure sensor to misread the system’s performance.
- Low System Pressure
If the system pressure is consistently low, the boiler will have trouble detecting the required pressure rise when the pump activates. While low pressure may seem minor, it can lead to frequent F75 faults and should be addressed promptly.
- Airlocks in the Pump or Heating System
Airlocks are pockets of air trapped within the boiler or heating system, preventing the pump from circulating water effectively. After bleeding radiators or refilling the system, airlocks can sometimes develop, making the pump work harder and triggering the F75 error.
- Sensor Sensitivity
Older Vaillant and Glow-worm boilers often have more sensitive pressure sensors prone to failure. Over time, these sensors can become unreliable, causing the F75 fault even when there isn’t a significant issue with the system.
- Inadequate Maintenance
Lack of regular boiler servicing is one of the most common reasons for frequent F75 errors. Regular servicing helps prevent the buildup of sludge, debris, and limescale, which can block the pressure sensor and affect pump performance. Skipping maintenance increases the likelihood of issues going unnoticed until they trigger a fault like F75.
- Boiler Age and Wear
As boilers age, their components naturally wear out. This is particularly true for the pump and pressure sensor, which are prone to failure after years of operation. As these components degrade, F75 faults are likely to occur more frequently.
- Cold Weather and Pressure Drops
During cold weather, the water in the system can contract, leading to a drop in pressure. This can exacerbate existing pump or pressure sensor issues, making F75 faults more likely in winter.
How to Resolve the F75 Fault
If your Vaillant or Glow-worm boiler displays the F75 error code, it’s essential to resolve it promptly to avoid further damage or extended downtime. Here are the most common solutions:
- Replace the Pressure Sensor
In many cases, a faulty or blocked pressure sensor is the leading cause of the F75 fault. Replacing the sensor can quickly restore your boiler’s functionality. Ensure a qualified engineer handles this, which involves working with sensitive components.
- Check and Clean the Pump
If the pump is blocked, worn out, or not functioning correctly, it may need to be cleaned or replaced. If the pump is still functional but has blockages due to sludge or debris, a power flush can help clear the system and restore average circulation.
- System Flush
Over time, sludge buildup in your central heating system can cause blockages that affect the pump and pressure sensor. A system flush (or power flush) removes this buildup, improving the overall performance of your heating system and reducing the likelihood of F75 faults.
- Regular Servicing
Routine boiler servicing is essential for preventing issues like the F75 fault. A qualified engineer can clean and check components like the pressure sensor, pump, and internal pipes, ensuring your boiler runs efficiently and preventing future breakdowns.
- Check System Pressure
Ensure your boiler’s pressure is within the manufacturer’s recommended range (typically between 1.0 and 1.5 bar). You may need to top up the system if the pressure is too low. If the issue persists, contact a professional to investigate further.
Final Thoughts
While the F75 fault is a common issue in Vaillant and Glow-worm boilers, it is usually a straightforward fix when handled by a professional. Regular maintenance, including flushing the system and replacing ageing components, can significantly reduce the likelihood of encountering this error.
If you’re experiencing persistent F75 faults or need assistance with your boiler, always seek help from a Gas Safe registered engineer. Proper care and servicing will keep your boiler running efficiently, saving you time and hassle in the long run.
By understanding the causes and solutions for the F75 fault, you can keep your Vaillant or Glow-worm boiler functioning smoothly, ensuring reliable heating and hot water throughout the year.
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