The Vaillant F28 fault code (shown as F.28 on some displays) means the boiler tried to light the burner at start-up but couldn’t get a flame, so it locked itself out. The cause is usually either a gas supply problem or an ignition problem inside the boiler. You can check the gas supply and, in cold weather, the condensate pipe yourself. Anything involving the gas valve, electrodes or the inside of the boiler needs a Gas Safe registered engineer.
| Question | Answer |
|---|---|
| What it means | Ignition failed during start-up |
| Common causes | Gas supply problem, frozen or blocked condensate pipe, faulty ignition parts or gas valve |
| First checks | Is gas reaching the property, is the condensate pipe frozen, is anything blocking the flue |
| Can you fix it yourself? | Only the basic checks and one reset. Repairs need an engineer |
| Is it dangerous? | The lockout is a safety shutdown, but gas and ignition faults need a qualified engineer |
What Does the Vaillant F28 Fault Code Mean?
When the boiler calls for heat, it opens the gas valve and tries to light the burner with an ignition spark. If no flame is detected, it repeats the attempt a few times and then locks out and shows F28. Vaillant describes this as a failure during start-up with unsuccessful ignition. F28 appears on many Vaillant models, including the ecoTEC range, but codes can vary between models, so check your manual if your display looks different.
F28 is a different fault from F29. F28 means the burner never lit at start-up, while F29 means the boiler lit, then lost the flame or failed to re-ignite while running. The checks overlap, but they are separate codes.
Common Causes of the Vaillant F28 Fault Code
| Cause | What It Can Look Like | Who Deals With It |
|---|---|---|
| Gas supply interruption (supplier work, closed isolation valve, meter fault, empty prepayment meter) | Other gas appliances, such as the hob, also don’t work | You can check the meter and valve. Gas supplier or engineer for faults |
| Frozen or blocked condensate pipe | F28 in cold weather, gurgling from the pipe outside | You can thaw an external pipe safely. Engineer if it keeps happening |
| Worn or faulty ignition electrodes or ignition system | No clicking spark, or clicking but no flame | Engineer |
| Faulty gas valve or low gas pressure | Boiler clicks and tries to light, but gas doesn’t reach the burner properly | Gas Safe engineer |
| Blocked flue or air intake | Debris, nests or damage at the flue outlet | You can look from outside. Engineer to clear or repair |
| Loose or damaged wiring, or a control board fault (less common) | Intermittent faults, F28 returning with no clear pattern | Engineer |
Gas Supply Problems
If gas isn’t reaching the boiler, the burner can’t light. This can come from supplier work in your area, a closed isolation valve, a meter fault, or a prepayment meter that has run out of credit. Air in the gas line after work on the supply can have the same effect. It’s the first thing to rule out because it’s quick to check.
Condensate Pipe Problems
Condensing boilers drain acidic water through a condensate pipe, usually a small white plastic pipe that runs from the boiler through an outside wall to a drain. In some homes it connects into a sink’s waste pipe. If it freezes or blocks, the boiler can lock out and show F28. This is a common cause in cold weather, especially if the boiler sat unused during a cold spell or part of the pipe runs outside. Gurgling or bubbling from the boiler while it runs can be another sign. A blocked condensate pipe isn’t limited to winter, so it’s worth mentioning to your engineer.
Ignition and Gas Valve Faults
Worn electrodes, a failing ignition system or a faulty gas valve can stop the flame from forming even when gas is available. Loose wiring or, less often, a control board fault can cause the same code. These all sit inside the boiler, so they are engineer jobs.
How to Fix a Vaillant F28 Fault: What You Can Check Yourself
Stay on the outside of the boiler and take these in order. If you’re unsure about any step, stop and call an engineer.
Step 1: Check the Gas Supply
If you can smell gas, skip this step and follow the gas emergency advice further down. Otherwise, turn on another gas appliance, such as the hob. If it doesn’t light either, the problem is likely the gas supply. Check that the gas isolation valve is open (the handle sits in line with the pipe when open) and, if you have a prepayment meter, that it has credit. If the supply has failed, contact your gas supplier.
Step 2: Check the Condensate Pipe in Cold Weather
If it’s freezing and part of the condensate pipe runs outside, look for ice or frost, especially at the end of the pipe and at bends where the insulation is thinnest. Thaw it by pouring warm water over the frozen section with a jug or watering can, or by holding a hot water bottle against it. Never use boiling water, which can crack the pipe. Only attempt this if the pipe is safely accessible from ground level. If F28 persists after thawing, stop resetting and contact an engineer, as the condensate trap or other internal parts may also need attention.
Step 3: Look at the Flue From Outside
Check the flue outlet for leaves, debris or anything blocking it. Don’t dismantle or poke anything. If you can see damage or a blockage, leave it for an engineer.
Step 4: Reset the Boiler Once
Follow the reset steps in your manual. If F28 comes straight back, stop there. Resetting only clears the message, and repeating it won’t fix a gas or ignition fault.
Never open the boiler casing or touch the gas valve, burner, electrodes, wiring or circuit board. That work needs a Gas Safe registered engineer.
If You Smell Gas or Suspect Carbon Monoxide
Gas emergency: if you smell gas, don’t use electrical switches or try to reset the boiler. Open windows and doors if it’s safe, turn off the gas at the meter if you can, leave the property and call the National Gas Emergency Service on 0800 111 999 from a safe location.
Carbon monoxide emergency: if you suspect carbon monoxide exposure, get everyone into fresh air immediately. Call 999 for urgent medical help if anyone has symptoms such as headaches, dizziness or nausea, or may be seriously affected.
When to Call a Gas Safe Engineer
- F28 returns after you’ve checked the gas supply and reset once
- Gas is reaching the property but the boiler still won’t light
- You hear clicking but no flame forms
- The condensate pipe keeps freezing or blocking
- You see damage or a blockage at the flue
- Anything that means opening the casing
What an Engineer Will Check
An engineer will check gas supply and pressure at the boiler, test the ignition electrodes and wiring, inspect the gas valve, clear or test the condensate trap and pipe, check the flue and air intake, and test the control board if nothing else explains it. F28 only reports that ignition failed, so most of the job is working out why the flame isn’t forming.
How Much Does It Cost to Fix a Vaillant F28 Fault?
The cost depends on the cause. The gas supply and condensate checks above cost nothing. If an engineer is needed, BeFix charges £95 an hour from 7AM to 5PM, £125 from 5PM to 9PM and £160 from 9PM to 7AM, all exclusive of VAT, with no call-out fee. Parts are charged separately from labour, and your engineer will confirm the likely cost once they’ve diagnosed the fault. Clearing a blocked condensate pipe is a very different job from replacing a gas valve.
Do You Need a New Boiler for an F28 Fault?
Usually not. F28 is most often a gas supply, condensate or ignition part problem that can be fixed. A new boiler is worth considering only if the boiler is old, faults keep returning despite repairs, and the repair quote is getting close to the cost of a replacement. Your engineer can tell you whether a repair still makes sense, and BeFix can also advise on boiler installation in London.
Is the Vaillant F28 Fault Dangerous?
The lockout itself is the boiler shutting down safely when it can’t light, so you’ll be without heating and hot water until it’s resolved. Gas and ignition faults shouldn’t be tampered with, so the cause needs a qualified engineer. Don’t keep resetting the boiler, and don’t try to bypass it. Have a Gas Safe registered engineer find and fix the cause.
Other Vaillant Fault Codes You Might See
Vaillant codes beginning with F are faults that stop the boiler working. Your manual lists the full set for your model.
| Code | Meaning | Can You Fix It Yourself? | Full Guide |
|---|---|---|---|
| F22 | Low system pressure | Often, by topping up through the filling loop | Vaillant Boiler F22 Error Code |
| F23 | Temperature difference between flow and return too large, usually poor circulation | Partly. Bleeding radiators can help, but most causes need an engineer | Vaillant F23 Fault Code |
| F28 | Ignition failed at start-up | Basic checks only, then an engineer | This guide |
| F29 | Flame lost or re-ignition failed while running | Basic checks only, then an engineer | No guide yet |
| F62 | Gas valve closing late or flame detected when it shouldn’t be | No, needs a Gas Safe engineer | Vaillant F62 Fault Code |
| F75 | Pressure sensor or pump related fault | No, needs a Gas Safe engineer | No guide yet |
| F83 | Little or no temperature rise after the burner starts (dry fire) | Sometimes, depending on the cause | Vaillant F83 Fault Code |
How to Avoid F28 Coming Back
An annual service with a Gas Safe registered engineer can catch worn electrodes, condensate build-up and early gas valve problems before they cause a lockout, and many manufacturer guarantees require one, so check the terms of yours. In cold weather, keep an eye on any external condensate pipe, and make sure the flue outlet stays clear of debris. Once a frozen pipe has thawed, fit pipe lagging from a DIY store around the exposed section. If you’re going away in winter, keeping the heating on a timer helps stop the pipe freezing. Your engineer can also tell you whether a pipe that freezes often needs rerouting.
Book a BeFix Engineer for a Vaillant F28 Fault
BeFix provides boiler fault diagnosis and boiler repair in London, including Vaillant F28 faults. Our Gas Safe registered engineers will find out why the burner isn’t lighting and fix it safely.
We offer same-day appointments, subject to availability, and engineers typically arrive within 1 to 3 hours. All repair work comes with a 12-month workmanship warranty. A photo of the display and your boiler model and serial number help us prepare.
You can also book a boiler repair online, call 020 8058 4241 or email info@befix.co.uk with photos. We’re open Mon to Fri 7AM to 10PM and Sat and Sun 9AM to 8PM. BeFix is at 227B Nether Street, London N3 1NT.
FAQs
What does the Vaillant F28 fault code mean?
F28 means the boiler failed to ignite during start-up. It tried to light the burner, no flame was detected, and it locked out as a safety measure. The cause is usually a gas supply problem or a fault in the ignition system, gas valve or condensate drain.
How do I fix a Vaillant F28 fault?
Check that gas is reaching the property by trying another gas appliance, check for a frozen condensate pipe in cold weather, look for a blocked flue from outside, then reset the boiler once following your manual. If F28 returns, you’ll need a Gas Safe registered engineer.
How do I reset a Vaillant F28 fault code?
Follow the reset steps in your manual for your model, and only do it once. If F28 comes straight back, the cause is still there, so stop resetting and call an engineer.
Is the F28 fault dangerous?
The lockout is the boiler shutting down safely, but the cause can involve gas or ignition parts, so don’t try to repair them yourself. If you smell gas, treat it as an emergency and call the National Gas Emergency Service on 0800 111 999.
What’s the difference between F28 and F29?
F28 means the burner failed to light at start-up. F29 means the boiler lit but then lost the flame, or failed to re-ignite while running. The causes and first checks overlap, but they are separate faults.
Why does my F28 fault keep coming back?
A reset only clears the message. If F28 returns, the cause is still there. A gas supply issue, a frozen or blocked condensate pipe, worn electrodes or a faulty gas valve could all be behind it, so the boiler needs a proper diagnosis.
Why do I still get F28 when my hob works?
A working hob suggests gas is reaching the property, but it doesn’t confirm the boiler is getting enough gas pressure. F28 could still come from a restriction in the gas supply to the boiler, a frozen or blocked condensate pipe, worn electrodes or a faulty gas valve. Check only the accessible outside parts, reset once following your manual, and call a Gas Safe registered engineer if the fault returns.
Can I keep pressing reset?
No. Reset once following your manual. If F28 comes back, the cause is still there, and repeated resets won’t fix it.
Can I fix the F28 fault myself?
You can check the gas supply, thaw an external condensate pipe with warm water, look at the flue from outside and reset once. The gas valve, electrodes, wiring and anything inside the casing are jobs for a Gas Safe registered engineer.
How much does it cost to fix a Vaillant F28 fault?
The basic checks are free. If an engineer is needed, BeFix charges £95 an hour from 7AM to 5PM, £125 from 5PM to 9PM and £160 from 9PM to 7AM, exclusive of VAT, with no call-out fee. Parts are charged separately from labour.
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