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A Vaillant F28 fault code can leave you without heating and hot water, often at the worst possible time. If your Vaillant boiler has suddenly stopped working and is displaying this error code, don’t panic—it’s a common issue that can often be diagnosed and resolved with the right approach.
In this blog, we’ll explain:
✅ What the F28 fault code means
✅ The most common causes of the issue
✅ Step-by-step troubleshooting methods
✅ The cost of fixing an F28 fault and when to call an engineer
By the end, you’ll have a clear understanding of what’s causing the problem and how to fix it safely and efficiently.
If your boiler has developed an F28 fault, you will notice the following:
🚨 Complete loss of heating and hot water – The boiler will not function at all until the issue is resolved.
🚨 Multiple failed ignition attempts – The boiler will attempt to ignite three times but will fail each time before displaying the F28 fault code on the screen.
🚨 Clicking noises from the boiler – In some cases, you may hear the ignition electrodes clicking repeatedly as the boiler tries to fire up.
🚨 No visible flame in the boiler. The boiler’s burner will remain unlit, confirming an ignition failure.
Modern boilers have built-in safety mechanisms that automatically shut down the system when they detect a fault that could lead to a potential hazard. In the case of F28, the boiler cannot detect a flame, which could mean:
❌ There is no gas supply reaching the boiler.
❌ The ignition system is faulty and unable to spark the burner.
❌ A blockage in the system is preventing safe ignition.
If the boiler did not shut down under these conditions, it could risk leaking unburned gas, which poses a serious safety hazard. This is why the F28 fault should never be ignored or repeatedly reset without professional inspection.
💡 Important: Since this fault is typically related to gas supply, ignition failure, or a frozen condensate pipe, it is not always a fixable issue for homeowners. In most cases, a Gas Safe engineer will be required to safely diagnose and repair the fault.
Several factors can prevent your Vaillant boiler from igniting. The most common causes include:
If your boiler isn’t receiving gas, it won’t be able to ignite. This could be due to:
Gas meter problems (especially if you’re on a prepaid meter and credit has run out).
Gas valve failure inside the boiler, preventing gas from reaching the burner.
Low gas pressure from the mains supply, particularly during extreme cold weather.
A blocked gas pipe due to debris or a mechanical fault.
Ensure your gas supply is working by checking if other gas appliances (such as a gas hob) are functioning.
If you have a prepaid gas meter, make sure you have enough credit.
Contact your gas supplier to check if there are supply issues in your area.
💡 If you suspect a gas supply issue, you will need a Gas Safe engineer to inspect your system.
In cold weather, the condensate pipe (which removes waste water from the boiler) can freeze, causing a blockage. When this happens, the boiler may fail to ignite because the safety mechanism prevents operation if wastewater can’t drain properly.
Locate the white plastic condensate pipe leading outside.
If temperatures are freezing, the pipe may be blocked with ice.
Gently thaw the pipe by pouring warm (not boiling) water over it.
Wrap the pipe in insulation to prevent freezing in the future.
💡 This is one of the most common causes of the F28 fault in winter.
The ignition electrodes generate the spark needed to ignite the gas. If they are worn out, dirty, or misaligned, the boiler may struggle to ignite.
If the boiler makes repeated clicking noises but doesn’t fire up, this could indicate an ignition fault.
If the electrodes are covered in carbon deposits or corroded, they may need replacing.
A Gas Safe engineer can clean or replace the ignition electrodes if necessary.
The gas valve controls the flow of gas to the burner. If it’s faulty or stuck in a closed position, the boiler won’t receive enough gas to ignite.
✔ The boiler tries to ignite but fails multiple times.
✔ There’s no visible flame when the boiler attempts to fire up.
✔ The gas valve may be stuck or not opening properly.
A Gas Safe engineer will test the gas valve and replace it if necessary.
💡 Gas valve issues require professional repair—do not attempt to fix this yourself.
A blocked burner or flue can prevent the boiler from venting gases properly, stopping it from igniting.
Dirt or carbon buildup on the burner.
A blocked flue prevents proper ventilation.
A Gas Safe engineer can clean the burner and inspect the flue for obstructions.
Since the F28 fault is related to gas and ignition, most of the solutions require a Gas Safe engineer. However, there are some simple checks you can do before calling for help.
Check your gas supply – Make sure your gas is on and test other appliances such as a gas hob or cooker. If the gas hob works, then it is specifically your boiler which is not working.
✅ Thaw the condensate pipe – If it’s frozen, carefully thaw it with warm water.
✅ Reset the boiler – Press and hold the reset button for 3-5 seconds and see if the boiler reignites.
✅ Check for gas supply issues in your area – Call your gas provider if needed.
💡 If none of these steps work, or if you suspect an internal component failure, contact a Gas Safe engineer for a professional inspection.
The cost of repairing an F28 fault will depend on what’s causing the problem. Here’s a rough estimate of the potential costs:
Fault | DIY Fix? | Estimated Cost |
Thawing a frozen condensate pipe | ✅ Yes | £0 |
Checking gas meter and supply | ✅ Yes | £0 |
Ignition electrode replacement | ❌ No | £80-£150 |
Gas valve replacement | ❌ No | £150-£400 |
Flue or burner cleaning | ❌ No | £80-£200 |
Full boiler servicing (recommended) | ❌ No | £80-£120 |
💡 If your boiler is over 10 years old and frequently displaying the F28 fault, it may be worth considering a replacement rather than ongoing repairs.
The Vaillant F28 fault code is a serious issue that indicates an ignition failure, meaning your boiler is not safely igniting gas. This could be due to a faulty gas valve, ignition electrodes, a blocked burner, or a problem with the gas supply itself. Because these components are critical to the safe operation of your boiler, only a qualified Gas Safe engineer should carry out any repairs or inspections.
🚨 Do NOT attempt to open the boiler or fix internal components yourself – working on gas appliances without the correct qualifications is extremely dangerous and can put you at risk of gas leaks, fires, or carbon monoxide poisoning.
✔ Check if your gas supply is on. If you have a gas hob, test whether it’s working. If there’s no gas supply to your property, contact your gas provider.
✔ If it’s winter, check your condensate pipe. If it’s frozen, carefully thaw it with warm water.
✔ Reset your boiler – Sometimes, a simple reset can clear the fault. Press and hold the reset button for 3–5 seconds.
✔ Call a Gas Safe engineer – If the issue persists, the problem is likely within the boiler’s internal components, which require professional attention.
🔹 Gas appliances must be handled by a Gas Safe registered engineer – Attempting to repair your boiler yourself could not only make the issue worse but also void your warranty.
🔹 The problem could indicate a serious safety risk – If your gas valve is faulty or your boiler is struggling to ignite properly, there is a risk of gas leaks or dangerous emissions.
🔹 A professional diagnosis ensures the correct fix – A Gas Safe engineer will inspect the ignition system, test gas flow, and check for blockages or faulty components to get your boiler running safely again.
🚨 Don’t take risks with gas appliances. If your Vaillant boiler is showing the F28 fault, contact a Gas Safe registered engineer immediately to ensure a safe and professional repair!
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