Vaillant F28 Fault Code: What is it & How to Fix it?

Oscar Garner

By Oscar Garner

Last Updated on June, 2024

It is a chilly winter’s day. You’re relaxing at home all cosy in your bed with a warm glass of hot chocolate and Netflix on your TV, when suddenly you feel the temperature in your room drop. 

Great. There seems to be a problem with your central heating system. Talk about a mood killer.

You sigh in defeat and check your Vaillant boiler to see what the issue is and notice the F28 error code on it. But what does it mean? 

Don’t worry; we’re here to help! In this article, we’ll be breaking down what the Vaillant F28 error code is, what causes the F28 error code and how to fix it, how to avoid the Vaillant F28 fault code from occurring, and so much more to know about your Vaillant boiler!

Having your central heating system break down during freezing weather is annoying, but with a few steps, you’ll be able to have your Vaillant boiler up and running again in no time.

Quick Summary

  • The F28 error code on Vaillant boilers means there is an ignition fault.
  • The issue can be caused by several internal problems, but is most commonly linked to a faulty gas valve or an ignition fault.
  • Regular maintenance and proper insulation can prevent the F28 fault code from occurring, and it is important to always contact a Gas Safe registered engineer for any technical issues.

What is the Vaillant F28 Error Code? 

a picture of the f28 error in a vaillant boiler

When your Vaillant boiler has a problem, it shows a three-digit code, like F28, on its screen. This code tells you what’s wrong, such as if a part isn’t working right. You can find the code on the display screen in the middle of your Vaillant boiler or under a panel at the bottom. 

The Vaillant F28 error code means the boiler has an ignition fault. This can happen if three ignition attempts have failed.

The issue can be tricky because it could be caused by several internal problems, but generally, the F28 fault code can be linked to a faulty gas valve and an ignition fault. For your Vaillant boiler to work, it needs to light the gas to make a flame that heats the cold water.

The gas valve controls the gas supply that goes into the boiler. If you get an F28 fault code, the boiler might go into ‘lockout,’ which means it shuts down to stop further problems.

You might be tempted to restart it immediately and return to that Netflix show you were watching, but it’s better to wait. 

Figuring out what’s causing the issue now can save you trouble later. It’s best to diagnose the problem correctly so that you can fix it thoroughly to avoid more boiler fails and further damage.

What Causes the F28 Fault Code and How to Fix it? 

During winter, the F28 error code is very common due to low boiler pressure or a frozen condensate pipe. Issues like these do not require the services of a gas-safe engineer, as you can easily fix them. 

Let’s look into some more reasons for this fault. 

There’s a Gas Valve Fault

When your Vaillant boiler needs gas, the gas valve opens and closes. However, if you have an old boiler, the gas valve might show signs of wear and tear, resulting in your gas valve sticking.

This mechanical fault stops the boiler from working right, and the faulty gas valve becomes the issue. 

You might have to replace the gas valve if there is a problem with it. This can cost you about £300, covering the new part and the work needed. At that price, you may want to consider buying a new boiler instead. 

The Frozen Condensate Pipe is Causing a Blockage

Frozen condensate pipes are caused when the condensate pipe in your boiler takes away extra water vapour from the combustion process. Because your Vaillant boiler is hot, the vapour turns back into water and can be disposed of along with other wastewater in your home. 

Sometimes, especially during cold weather in winter, these condensate pipes can get blocked, often due to freezing, if not insulated correctly. If this happens, it’s not too hard to fix. A gas-safe engineer can thaw it out with hot water, or you can do it yourself. 

If the condensate pipe gets blocked, you must clear it to get your Vaillant boiler working again and restore the gas flow pressure. 

How to Defrost the Frozen Condensate Pipe?

different types of vaillant boliers

If you suspect a frozen condensate pipe, try thawing it with hot water. Check if there’s a colder spot on the pipe, which could mean it’s blocked or frozen.

Carefully pour warm water from a kettle over the pipe, but watch out because if it’s freezing outside, the water might freeze on the ground, which can be dangerous. If you think it’s safe to try thawing the pipe using this method, wait a bit, then reset your Vaillant boiler. 

If your boiler starts working again, great! If not, calling a registered gas safe engineer for help is best. 

There’s an Electrical or Wiring Fault

The printed circuit board (PCB) in your boiler is like its brain, with all the parts connected electronically. If you have a faulty PCB, it might be covered by your Vaillant warranty, or it could just be plugged wrong. 

If a wire isn’t connected right or broken, you’ll have a problem. The ignition system might also be at fault, including parts like the ignition cable, ignition electrode, ignition transformer, or ignition plug. 

Sometimes, the wire connecting the spark electrode to the printed circuit board (PCB) gets damaged or worn out. To fix this issue, you can replace the spark electrodes. Gas safe engineers will be able to fix it right away for you.

The cost of Vaillant spark electrodes is about £24.59, and an ignition cable will be around £33.

Low Boiler Pressure

Your boiler might have low pressure, which could be from bleeding a radiator, which releases air and can drop the pressure, or there might be a water leak in the system. 

Most modern boilers, like Vaillant boilers, have a pressure gauge you can see. If the needle is in the green section, the pressure is good. If it’s below, it’s too low. 

Bleeding a radiator helps your heating work better but can lower the pressure. Check the pipes around your boiler for any signs of a water leak. If you can’t find anything, it’s best to call a registered gas safe engineer or book a Vaillant boiler service to check it out.

They might need to repressurise the system. You can do it yourself with a few simple steps. 

How to Repressurise Your Boiler to Fix the F28 Fault Code? 

First, find the pressure gauge and filling loops on your boiler. They should be at a right angle to each other. Turn off your boiler, then align the loops with the pipe at a 90-degree angle. 

Wait until you hear the water and watch the pressure gauge. Once the needle is back in the green zone, turn the loops back to 90 degrees and switch your boiler back on. Check if the pressure stays steady. 

If it’s okay, your heating system should be working again. If not, call a registered gas safe engineer to find the issue. Other problems might be the gas pressure regulator, a faulty gas metre, or the wrong gas restrictor. 

You might also see symbols like an egg timer on your Vaillant boiler, which could be normal unless it flashes. 

There Could Be an Issue With the Gas Supply

If you see the F28 fault code on your boiler, it might mean there’s a gas supply fault. Check if the other gas appliances in your house are working. If not, the issue is most likely with your gas supplier, not your boiler. 

If you’re on a pre-paid metre, try making a payment and then resetting your boiler. This could fix the problem. However, if the other gas appliances in your house are working fine, the F28 error code means there’s a problem with your boiler. 

How to Fix the Vaillant Boiler F28 Error Code? 

a picture of the f28 error in a vaillant boiler

If your boiler shows the F28 error code, it’s best to contact a gas-safe engineer for help. They can figure out what exactly is wrong and find the right solution to get your boiler and heating system working again. 

Sometimes, if it’s an issue with the gas valve or gas supply, you might be able to follow instructions to fix it yourself. However, if it’s a more complicated problem, you’ll need the help of a qualified engineer. 

Do I Need a Gas Safe Engineer to Fix the F28 Fault Code on My Vaillant Boiler?

Yes, you do. Never try to fix your boiler yourself if the problem is technical. It’s important to call a gas-safe registered engineer because they are fully trained and licensed to repair Vaillant boilers. 

Sometimes, you might be able to solve the problem yourself, but if you’re not sure, it’s best to seek professional help. 

The heating engineer can tell you if it’s better to repair your current boiler or replace it with a new one, depending on the seriousness of the problem and how old your boiler is. 

Will I Need to Replace My Vaillant Boiler?

Not necessarily. After all, Vaillant boilers aren’t cheap. You might not need a new boiler right away. Your gas-safe registered engineer will find out what’s causing the F28 fault code and let you know the options available.

If you’re worried about the cost of a new boiler, consider getting one in instalments to spread out the payments. If you’re dealing with a broken boiler or one that is too old and giving you problems, replacing it might be cheaper in the long run. 

Ensure your boiler is serviced regularly to keep it in good working condition. Keep your warranty paperwork safe in case of an issue. 

How to Prevent the Vaillant F28 Error From Occurring?

Boilers can develop faults over time. They aren’t meant to last forever. To save money, carry out regular maintenance and upgrade it when you can. Consider insulating your condensate pipe and changing your gas valves for better efficiency.

Other Vaillant Error Codes 

a plumber fixing a water heater

The F28 fault code isn’t the only error your boiler can experience. Below is a list of error codes that can help you control any issues with your boiler. 

  • F.00: Heating Flow Temperature Sensor Interruption.
  • F.01: Failure To Ignite.
  • F.02: An Issue With The Flame During Normal Operations.
  • F.03: A Fault In The Fan. 
  • F.10: Flow NTC Short Circuit. 
  • F.11: A Short Circuit On The Heating Return NTC Thermistor. 
  • F.12: Issue With Your Heating Flow Thermister (NTC) And Sensor Plug. 
  • F.13: Issue With Your Heating Flow Thermister (NTC). 
  • F.20: Overheating. 
  • F.22: The Water Pressure Has Fallen Low. 
  • F.23: Safety Shut Down Due To Excessive Temperature Variation. 
  • F.24: Not Enough Water In The Boiler. 
  • F.25: The Flow Temperature Has Gone Up Too Quickly. 
  • F.26: The Gas Valve Activated Via The Gas Stepper Motor Has Stopped Working. 
  • F.27: An Incorrect Flame Has Been Detected. 
  • F.28: Ignition Or Gas Valve Problems. 
  • F.29: Flame Failure. (Read more about it here.)
  • F.32: Fault In The Air System. 
  • F.49: An Issue With The eBus Connection. 
  • F.52: Connection Fault With The Mass Flow Sensor. 
  • F.53: Flow Sensor Function Is Faulty. 
  • F.54: Not Receiving The Gas Quantities Needed To Ignite The Flame. 
  • F.56: Gas Valve Defective. 
  • F.57: The Ignition Electrode Is Corroded. 
  • F.61:  A Fault With Either Your Gas Valve, The Wiring Harness, Or The PCB. 
  • F.62: The Gas Valve Hasn’t Closed When The Boiler Is Turned Off. 
  • F.63: Problem With The PCB.
  • F.64: The Flow And Return Sensors Are Defective. 
  • F.65: Overheated Electronics. 
  • F.67: Electronic Fault In The Flame System. 
  • F.68: Unstable Flame Signal. 
  • F.70: The PCB Has Not Been Assigned It’s Software Identity For The Model Of Boiler It Is Intended For. 
  • F.71: Disconnected Or Defective Heating Flow NTC Thermistor. 
  • F.72: The Communication Between The PCB/ Thermistors Is Damaged Or Faulty Wiring.
  • F.73: No Communication Between The Pressure Sensor And The PCB. 
  • F.74: The PCB Is Detecting A Short Circuit Or Excessively High Voltage Back From The Pressure Sensor. 
  • F.75: Your Boiler Can’t Register A Pressure Change When The Pump Turns On. 
  • F.76: Too Much Heat Stress Being Applied To The Primary Heat Exchanger. 
  • F.77: No Response From The Flue. 
  • F.78: Interruption To DHW Outlet Sensor At External Controller, Link Box Is Connected, But Hot Water NTC Is Not Bridged. 
  • F.80: actoSTOR Inlet Sensor Fault. 
  • F.81: Lack Of Hot Water. 
  • F.83: The Boiler Detected A Temperature Difference In The Return Or Flow Pipes.
  • F.84: The Boiler Detected A Permanent Temperature Difference Between Flow And Return Pipes.
  • F.85: Error With Flow And Return Temperature, Sensor Incorrectly Fitted. 
  • F.90: Communication With actoSTOR Module Has Been Interrupted. 
  • F.91: Lack Of Hot Water. 
  • F.92: The Coding Resistor On The PCB Does Not Match The Gas Group That Is Entered. 
  • F.93: Gas Group Fault. 


Yes, you can reset your Vaillant boiler to resolve the F28 fault by manually resetting it after the issue has been fixed and checked by a registered heating engineer. Otherwise, if the problem has not been resolved, the error code will continue to appear if you attempt to reset it too soon.


Having your heating system down during a particularly cold day can be annoying. Be it a faulty gas valve or an issue with your gas supply, we have covered why your boiler is showing the F28 error code. 

If the problem is more complicated than you thought it was, be sure to contact a Gas Safe engineer to handle any technical issues. 

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