And you thought 27 was bad. Welcome to the emporium of Vaillant F28. Let's explain this fault, and who's at fault.
- What does F28 mean on a Vaillant boiler?
- What causes a Vaillant F28 fault code?
- Which Vaillant boilers show the F28 error code?
- Can I Fix This Error Fault Code Myself?
- Do I Need to Contact a Gas Safe Engineer to Fix the F28 Fault Code?
- Common reasons why the Vaillant F28 error code appears
- How do I fix F28 on my Vaillant boiler?
- How Much Will It Cost To Repair The F28 Fault Code?
- F28 vs F29: what’s the difference?
- Do You Need A New Boiler?
A Vaillant F28 fault code means your boiler failed to ignite and didn’t detect a flame, so it has locked out after failed ignition attempts.
Delve down below to reveal your immediate boiler destiny and the reason you're this deep in Google.
It's most likely going to need a boiler engineer visit (but there is one reason which might save you that fate).
Do this now (safe homeowner checks):
[1] Check if you have gas at all
Turn on another gas appliance (hob/fire).
If nothing works - it’s likely a gas supply / meter / credit issue, not the boiler.
If other appliances work - the issue is likely inside the boiler system (ignition, condensate, flue, etc.) and you’ll probably need an engineer - but you can still do the checks below.
[2] If it’s freezing outside, check the condensate pipe
In winter, the condensate pipe can freeze and block the boiler, which can trigger ignition/lockout faults.
[3] Reset the boiler once (not 14 times)
Try a single reset following your boiler manual.
If F28 returns, stop there - repeated resets won’t magically “convince” the boiler. It’ll just keep failing, and you’ll keep developing new emotional damage.
🔑 Key takeaways:
What F28 means - ignition failure / no flame detected → boiler locks out.
Most common causes - gas supply issue, frozen/blocked condensate pipe, ignition electrode fault, flue/air intake problem.
Safe DIY checks - confirm gas supply, check condensate pipe (in freezing weather), reset once.
Call a pro - if it returns after checks, you need a Gas Safe engineer.
Sometimes replacement makes more sense - especially if the boiler is old or breaking down often.
What does F28 mean on a Vaillant boiler?
F28 means the boiler can’t ignite properly (it fails to establish a flame) and locks out after failed ignition attempts.
Ignition is the “spark → flame” moment. No flame = no heating hot water = no heating your home.
The boiler turns itself off as a safety measure because “letting gas flow without a stable flame” is the sort of thing that makes engineers sweat.
What causes a Vaillant F28 fault code?
There are lots of possible triggers, but they generally fall into two buckets:
Gas isn’t reaching the burner properly
The boiler can’t ignite it or can’t prove there’s a flame
Here are the most common culprits (in the order we see them most often).
Which Vaillant boilers show the F28 error code?
The Vaillant boiler F28 error code is displayed on the following Vaillant boiler models:
ecoTEC Pro Plus
Turbomax Plus 824/828E
(If you’re unsure, the model name is usually on the front panel or inside the flap.)
Think you may have an ongoing issue with your boiler? Check our list of the top 10 boiler problems common in all types of boilers.
Can I Fix This Error Fault Code Myself?
Before calling a professional, you can try a few simple DIY checks and fixes to potentially resolve the issue:
Inspect the flue for obstructions – Ensure there are no blockages that could be restricting airflow, as this can prevent the boiler from igniting properly.
Verify the gas supply – Check that your home’s gas supply is functioning correctly by testing other gas appliances. If they are working, the issue is likely boiler-specific.
Reset the boiler – Follow the manufacturer’s instructions to perform a reset, which may temporarily resolve the fault and restore heating.
❌ Don’t do this
Don’t open the boiler casing
Don’t attempt repairs to the gas valve, burner, ignition wiring, or PCB
Don’t repeatedly reset it over and over
If it persists, you need a Gas Safe engineer. Legally. And practically.
Do I Need to Contact a Gas Safe Engineer to Fix the F28 Fault Code?
Do I need a Gas Safe engineer for Vaillant F28?
If the boiler still shows F28 after the checks above, yes - you should book a Gas Safe registered engineer.
Gas faults and ignition faults can be dangerous if handled incorrectly, and many repairs will void warranties if done by anyone not qualified.
In other words: this is not the time for “I watched a YouTube video once.”
Common reasons why the Vaillant F28 error code appears
When diagnosing the cause of the f28 fault code on your boiler, a registered Gas Safe Engineer will likely inspect the following boiler components:
[1] Gas supply issue (the boring but common one)
If there’s no gas supply to the boiler, it can’t ignite. Very rude, but predictable.
How to test:
Try another gas appliance (hob/fire)
Possible reasons you’ve got no gas:
Your supplier is doing work or has cut supply
Your gas meter has an issue
You’re on prepay and you’ve run out of credit (it happens to the best of us)
An isolation valve is shut
Likely fix: restore gas supply / top up meter / supplier support
Cost to fix: varies (sometimes £0, sometimes you’re on the phone listening to hold music)
Looking to pay for your new boiler monthly? Refer to our boilers on finance guide.
[2] Frozen condensate pipe (winter’s favourite hobby)
The condensate pipe carries acidic wastewater away from the boiler. In freezing temperatures, that pipe can freeze, block, and cause the boiler to shut down.
This one is annoyingly common in winter - and it’s also the one that can sometimes save you an engineer callout.
Image showing a standard condensate pipe
Signs it might be frozen:
Very cold weather
Boiler has stopped suddenly
No heating/hot water
You can see/feel ice on the external plastic pipe
What to do:
Thaw the pipe using warm water (not boiling)
Use a hot water bottle or warm cloths
Once thawed, reset the boiler once
Cost to fix: £0 if you DIY, ~£50–£100 if an engineer visits
Bonus tip: if your condensate pipe is poorly routed externally, an engineer can re-route/insulate to reduce freezing risk.
You can attempt to do this yourself too, check out our quick DIY YouTube video below:
Additionally, modern boilers such as Worcester Bosches Greenstar Range are equipped with CondenseSure, this is a feature designed to prevent condensate pipes from freezing.
Cost to fix: £50-100
[3] Faulty gas valve (the “fuel tap” problem)
The gas valve controls gas flow into the boiler. If it fails (mechanically or electrically), gas won’t flow properly - and ignition fails.
Image showing a standard gas valve
Fix: repair/replace gas valve (engineer only)
Typical cost: ~£150–£300
Uncle William’s “faulty gas valve” is a different topic and should be discussed only after he’s stopped putting onions in everything.
[4] Wiring or connection fault (boiler brain not getting the memo)
Boiler components communicate through wiring back to the PCB (the control board).
If a wire is loose, damaged, or poorly connected, the boiler can fail to complete ignition safely and lock out.
Image showing standard PCB
Fix: wiring repair or connector replacement
Typical cost: ~£100–£500 (depends on what’s involved)
Is your boiler leaking or losing pressure? Use our quick and easy tool to get your fixed price boiler replacement.
PS You may be interested in Gas Engineer Allen Hart explaining the most common boiler problems and how you can resolve them in the video below:
[5] Faulty ignition electrode (spark’s not sparking)
Ignition electrodes create the spark that lights the gas.
Over time they can wear, corrode, shift position, or fail - meaning the boiler can’t light the flame.
Image showing a standard electrode
Fix: clean, reposition, or replace electrode (engineer only)
Typical cost: ~£100–£300
Your electrodes didn’t “grow apart”… but if they did, we support them in their new journey.
Additionally, modern boilers such as Worcester Boschs Greenstar Range are equipped with CondenseSure, this is a feature designed to prevent condensate pipes from freezing.
[6] Flue / air intake issue (it can’t breathe properly)
Boilers need the correct airflow to ignite safely.
If the flue or air intake is obstructed or faulty, ignition can fail.
Safe homeowner check:
Visually check for obvious external blockages (leaves, nests, debris)
Don’t remove components or dismantle the flue
Fix: engineer inspection, cleaning, repair
Typical cost: varies
[7] PCB fault (less common, more expensive)
The printed circuit board is the boiler’s control centre. If it fails, it may incorrectly manage ignition, fail safety checks, or lock out.
Image showing a standard PCB
Check our new boiler costs guide and use our boiler size calculator if you want to get a better understanding of how our fixed-price boiler quote tool works.
How do I fix F28 on my Vaillant boiler?
If you’re experiencing the Vaillant F28 Boiler Fault code, it indicates a gas supply or ignition issue. You can try the following troubleshooting steps to resolve the issue:
Reset the boiler - Try resetting your boiler by turning it off and on again. Some models have a dedicated ‘reset’ button - refer to your user manual for instructions.
Check your gas supply - Ensure your gas supply is functioning by testing other gas appliances in your home. If they are working properly, the issue is likely specific to the boiler rather than the gas supply.
Inspect the flue and air intakes - Check for any blockages or obstructions in the flue or air intake pipes, as these can prevent the boiler from igniting.
Seek professional help - If the F28 fault code persists after trying these steps, it’s best to contact a Gas Safe registered engineer. The issue may be caused by a faulty ignition system, gas valve, or another internal component that requires expert diagnosis and repair.
How Much Will It Cost To Repair The F28 Fault Code?
A typical F28 repair often lands somewhere around £150–£300, but it depends on the cause.
Factors That Can Affect the Repair Cost:
Severity of the Issue - More complex faults, such as a faulty gas valve or ignition failure, may require additional time and costly replacement parts.
Location - Repair costs can vary significantly depending on your region, with higher rates often seen in major cities compared to rural areas.
Urgency of the Repair - Emergency or out-of-hours call-outs usually come with higher service charges.
Addressing boiler error codes promptly not only helps maintain the efficiency and safety of your heating system but can also prevent more costly repairs in the future.
F28 vs F29: what’s the difference?
F28: failed ignition / no flame detected (can’t light)
F29: flame was established but then lost (can’t keep it lit)
They’re cousins. Neither is invited to your dinner party.
Do You Need A New Boiler?
In some cases, replacing a boiler can make more financial sense than continuing to repair it. Here are the key factors to consider:
Age of the Boiler - If your boiler has surpassed its average lifespan (typically beyond 15 years) and is no longer covered by the manufacturer’s warranty, replacing it may be a more cost-effective option to avoid recurring repair expenses.
Repair Costs - When the cost of repairing the boiler exceeds 50% of the price of a new one, it’s usually more financially sensible to invest in a replacement rather than continuing with costly repairs.
Frequency of Breakdowns - If your boiler is breaking down more frequently, it’s often a sign of significant wear and tear and it is beyond economical repair. In such cases, replacing the boiler can help avoid mounting repair costs and the inconvenience of ongoing issues.
Energy Efficiency - Older boilers tend to be far less efficient than modern models, leading to higher running costs. Upgrading from a G-rated to an A-rated boiler could save you up to £385 per year in energy bills, making replacement a financially smart decision in the long run.
By carefully weighing these factors, you can determine whether replacing your boiler offers better value and peace of mind compared to continued repairs.
Learn all about combi boilers in our what is a combi boiler.
Get a Quote for a New Boiler Today
The best way to resolve the F28 error code is to seek the help of a registered Gas Safe Engineer, who will be able to diagnose and repair whatever is causing the f28 code to be displayed.
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