Troubleshooting Vaillant boiler fault codes: F75, F22, F27 & F28/29 explained

If you're seeing an error code like F75 , F22 , F27 , or F28/F29 on your Vaillant boiler , you’re not alone - these codes are common across many models and can disrupt your heating and hot water supply. While some faults may seem minor at first, ignoring them can lead to bigger problems down the line - including costly repairs or even safety risks.

At Fusion Plumbing & Electrical , we specialise in fast, reliable heating and boiler services across London. Our Gas Safe-certified engineers are trained to diagnose and resolve all types of boiler faults efficiently, helping both homeowners and landlords stay warm, safe, and stress-free throughout the year.

In this guide, we’ll explain what each fault means, how to identify potential causes, and when it’s best to call in the professionals.

🔧 F75 - No pressure change detected

The F75 error code appears when your Vaillant boiler detects that the pump is running but no pressure change is occurring in the system. This could indicate a faulty pump, a blocked sensor, or issues with the overall system pressure.

While a simple reset may resolve the issue temporarily, recurring F75 errors often point to deeper mechanical problems. In these cases, it's best to call a qualified Gas Safe engineer.

🔗 Book emergency heating repair if the issue persists after basic checks.

🔧 F22 - Low water pressure

The F22 error code is displayed when the boiler senses that system pressure has dropped below 0.5 bar. This can happen due to minor leaks , a natural pressure drop , or simply because the filling loop hasn’t been used in a while.

You can try topping up the pressure using the filling loop - but if the pressure drops again quickly, there may be a leak in the system. In such cases, it's important to have a professional locate and fix the source.

🔗 Book boiler servicing to ensure your system remains in good working order.

🔧 F27 - False flame detection

The F27 error code is triggered when the boiler’s flame sensor detects a flame where there shouldn't be one - or fails to detect one when there should be. This can be caused by a dirty or damaged sensor, wiring issues, or a problem with the control board.

Because this fault involves electrical components and gas flow, it's typically best left to a professional. Attempting to fix it without proper tools or knowledge can be dangerous.

🔗 Book boiler servicing for a full diagnosis and repair.

🔧 F28 / F29 - Ignition failure

The F28 (no ignition) and F29 (ignition cut-out) error codes appear when the boiler fails to ignite the burner. Common causes include a gas supply issue , worn ignition electrodes , or a blocked flue .

Before calling a technician, check your gas supply and ensure nothing is obstructing the flue. But if the problem continues, it's time to bring in the experts.

🔗 Book heating installation or repair to restore your boiler’s function safely and quickly.

⚙️ When to DIY vs Call an Engineer

Some boiler faults are simple enough to address with basic troubleshooting, while others require the skills of a qualified Gas Safe engineer. Here’s a quick guide to help you decide what to do next:

• If your boiler shows F22 (low water pressure) and the pressure gauge reads below 0.5 bar, try topping up the system via the filling loop. If the pressure drops again quickly, there may be a leak - book boiler servicing to locate and repair it.
• For F75 (no pressure change detected) , a brief reset might resolve the issue. But if the fault persists or the pump doesn’t run at all, don’t attempt further fixes - book emergency heating repair as soon as possible.
• F27 (false flame detection) involves electrical components and gas flow. This type of fault is best left to professionals. 🔗 Book boiler servicing for a full diagnosis and safe repair.
• F28/F29 (ignition failure) means your boiler is failing to light the burner. While a blocked flue or faulty electrode might be the cause, these issues can be dangerous to tackle without proper tools or training. 🔗 Book heating installation or repair to restore your boiler safely.

🛠️ Preventive Maintenance

To avoid future breakdowns and prolong the life of your boiler, consider:

• 🔁 Annual Boiler Servicing - Required to maintain most warranties and ensure optimal performance.
• 💨 Power Flushing - Removes magnetite build-up from older systems.
• 📦 Magnetite Filter Installation - Helps protect pumps and sensors from future damage.

🔗 Schedule annual boiler maintenance to keep your heating system running smoothly.

Choosing the Right Engineer

When dealing with boiler faults, it's essential to work with a Gas Safe-registered engineer . At Fusion Plumbing & Electrical, our team is not only certified but also experienced in handling Vaillant boilers specifically , ensuring accurate diagnosis and long-lasting solutions.

We offer:

• Fast response times
• Transparent pricing
• Labour guarantees
• Emergency call-outs available

🔗 View our heating services or reach out directly for assistance

📞 Need Help Today?

If you're seeing any of these fault codes - F75, F22, F27, or F28/F29 - and need assistance, don’t wait for the problem to get worse. At Fusion Plumbing & Electrical , we offer fast, reliable heating repairs across London, including Westminster, Brent, and Camden.

Our Gas Safe-certified engineers are ready to diagnose and fix your boiler safely and efficiently -with priority call-outs and transparent service options. 🔗 View our pricing and 🔗 book now to get started today.