A warm home and a hot shower are everyday comforts—until your Vaillant boiler suddenly flashes a fault code. Before you panic, take a deep breath! These error codes are simply your boiler’s way of telling you something needs attention. Today, in this guide, we will decipher them in detail.
Some issues, like low pressure, can be a quick DIY fix, while others require an expert’s touch. Either way, you’re in the right place. At Happy Dog Plumbing & Heating, we specialise in Vaillant boiler repairs, installation and maintenance. Our Gas Safe-registered engineers provide fast, reliable, and affordable service to keep your home warm and stress-free.
Call us on 02086822244 or email us hello@happydogplumbing.london to let us take care of your boiler worries!
“Stay warm, stay safe, and leave your boiler worries to Happy Dog Plumbing & Heating!”
Vaillant Boiler Fault Codes Explained: Causes And Solutions
When your Vaillant boiler displays a fault code, it’s essentially diagnosing itself and telling you what’s wrong. Understanding these codes can save you stress and help determine whether it’s a quick fix or if you need a professional Gas Safe engineer to step in.
Below, we discuss the most common Vaillant boiler error codes, their causes, and the following steps to take.
Error Code 1: F13 – Cylinder Temperature Sensor Short-Circuited
Problem: The sensor for measuring the hot water cylinder temperature failed.
Possible causes:
- The faulty electrical connection in the cylinder temperature sensor
- Defective cylinder temperature sensor
Solution: A professional heating engineer must diagnose and replace the sensor if necessary. Do not attempt to fix this yourself, as it involves electrical components. Instead, call experts.
Error Code 2: F20 – Overheating Safety Cut-Out
Problem: The boiler has overheated.
Possible causes:
- Insufficient water in the system
- Faulty flow or return temperature sensor
- Blocked pump or diverter valve
- Defective water pressure sensor
Solution: This is a job for a professional. Do not attempt to reset the boiler repeatedly, as this could cause further damage—contact experts for help.
Error Code 3: F22 – Low Water Pressure
Problem: Your boiler pressure is too low.
Possible causes:
- No water in the system
- Faulty water pressure sensor
- Defective pump
- Leaking or faulty expansion vessel
Solution: Try topping up the boiler pressure using the filling loop. If the problem persists, call experts for a thorough inspection.
Error Code 4: F23 – Temperature Differential Too High
Problem: The temperature difference between the flow and return pipes is excessive.
Possible causes:
- Air trapped in the system
- Faulty temperature sensors
- Blocked pump or diverter valve
Solution: Bleed the radiators to remove trapped air. If this doesn’t work, book an engineer.
Error Code 5: F25 – Flue Gas Temperature Too High
Problem: The boiler’s flue gases are overheating.
Possible causes:
- Faulty flue gas temperature sensor
- Blocked flue or ventilation issues
Solution: Do not use your boiler until a Gas Safe engineer has checked it. This issue can cause dangerous carbon monoxide leaks.
Error Code 6: F27 – False Flame Detection
Problem: The boiler is detecting a flame when it shouldn’t.
Possible causes:
- Faulty PCB (printed circuit board)
- Gas valve malfunction
Solution: Turn off the boiler immediately and call an expert.
Error Code 7: F28 – Ignition Failure
Problem: The boiler fails to ignite.
Possible causes:
- Gas supply issue (e.g., gas valve closed)
- Air trapped in the gas line
- Defective ignition components
Solution: Check that your gas supply is on. If your other gas appliances work fine but the boiler doesn’t call us for a professional diagnosis.
Error Code 8: F29 – Flame Loss
Problem: The flame keeps going out during operation.
Possible causes:
- Gas supply issues
- Blocked flue or ventilation problem
- Faulty ignition components
Solution: This Vaillant boiler fault code requires a gas-safe engineer to inspect your system.
Error Code 9: F61 – Gas Valve Control Fault
Problem: The gas valve isn’t working correctly.
Possible causes:
- Loose electrical connections
- Faulty PCB or gas valve
Solution: This needs a professional boiler repair. Do not attempt to fix this yourself.
Error Code 10: F62 – Delayed Flame Switch-Off
Problem: The gas valve isn’t shutting down correctly.Possible causes:
- Defective gas valve
- PCB failure
Solution: Turn off your boiler and call a heating engineer ASAP.
Error Code 11: F75 – Pressure Sensor/Pump Issue
Problem: The boiler isn’t detecting a pressure change when starting up.
Possible causes:
- Faulty water pressure sensor
- Defective internal heating pump
- Air in the system
Solution: You may be able to repressurise your boiler, but if the fault persists, you need professional assistance.
How To Prevent Boiler Faults & Keep Your Vaillant Boiler In Top Condition
Preventative boiler maintenance is key to avoiding costly repairs and extending the lifespan of your boiler. Here’s what you can do:
- Book an annual boiler maintenance – A professional check-up ensures your boiler runs efficiently.
- Monitor boiler pressure – Keep an eye on the pressure gauge and top it up if needed.
- Bleed your radiators – This removes trapped air, preventing uneven heating.
- Check for leaks – Small leaks can lead to low water pressure and system failures.
- Install a magnetic filter – This prevents sludge buildup, improving efficiency.
Need A Vaillant Boiler Repair, Maintenance Or Installation Service? Call Happy Dog Plumbing & Heating Today!
When your Vaillant boiler displays a fault code, you need an experienced and reliable engineer to restore your heating and hot water as quickly as possible. That’s where Happy Dog Plumbing & Heating comes in! We are:
- Gas Safe-Registered engineers – Ensuring safe and compliant boiler repairs.
- 50+ years of experience – Our team has handled everything from minor faults to major breakdowns.
- Fast & reliable service – We respond quickly to emergency boiler issues. Plus, we offer Vaillant boiler repair, maintenance, and installation services.
- Fixed, transparent pricing – No hidden fees—just honest, fair pricing.
- Expert advice and support – We guide you to the best solution for your boiler.
So, if your Vaillant boiler displays an error code, don’t panic! Our expert heating engineers can efficiently diagnose and fix the problem, whether it’s a pressure issue, ignition failure, or sensor fault.
Call us on 02086822244 or email us at hello@happydogplumbing.london to book an engineer online.
