Quick answer: The F62 fault code (shown as F.62 on some displays) means your Vaillant boiler detected a flame still burning after the burner should have shut down. The control board saw a delayed flame switch-off and locked the boiler out to keep it safe. This is a gas valve, PCB or ignition electrode fault, and it is not a homeowner repair under any circumstances.
Written by the engineering team at Edinburgh Boiler Company, Scotland’s number one boiler installer. We’re Gas Safe registered and Vaillant-approved, and F62 is a code we treat as a priority call-out rather than a routine one.
What does the F62 fault code mean on a Vaillant boiler?
F62 means the flame took too long to go out after the boiler commanded the burner off. Every time your boiler finishes a heating cycle, the PCB sends a signal to close the gas valve, and the flame should extinguish within a tightly defined safety window. If the flame sensor still reads a signal after that window closes, the boiler declares a fault and locks out.
Two things can produce that reading, and they matter for very different reasons:
- Gas really is still flowing. The valve isn’t closing quickly enough, so the burner keeps firing after it should have stopped.
- Gas has stopped, but the boiler thinks it hasn’t. A degraded electrode or a misreading control board reports a flame signal that isn’t really there.
The boiler can’t tell the difference, so it assumes the worst and shuts everything down. That’s the system working correctly. An uncontrolled burner is exactly the scenario every safety interlock in a modern condensing boiler exists to prevent.
Why is F62 more serious than most other fault codes?
F62 sits on the gas side of the boiler, which puts it in a different category from circulation or pressure faults. Codes like F22 or F23 mean water isn’t moving properly. Annoying, potentially expensive, but not dangerous in themselves. F62 involves the gas valve and the flame control chain, which is the part of the appliance that keeps combustion contained and predictable.
This is why we tell customers to stop after one reset. With a circulation fault, repeated resets mostly just wear out the heat exchanger. With F62, repeated resets are asking a gas valve you already have reason to distrust to keep operating. Note the code, reset once, and if it comes back, switch the boiler off at the isolator and pick up the phone.
What causes an F62 fault on a Vaillant ecoTEC?
Vaillant lists three official causes: a defective gas valve, a defective PCB, or a defective ignition electrode. In the field we’d add wiring and connectors to that list, because a corroded plug behaves exactly like a failed component from the board’s point of view.
| Cause | How common | What’s actually happening | Typical fix |
|---|---|---|---|
| Slow or sticky gas valve | Very common | Heat cycling, age or debris stops the valve seating quickly | Gas valve replacement |
| PCB fault | Common | Board misreads the flame signal or sends the close command late | PCB replacement and reprogramming |
| Condensate or moisture on the PCB | Common on older units | A leaking trap or condensate pipe drips onto electronics and corrodes tracks | PCB replacement plus fixing the leak |
| Worn or cracked ignition electrode | Common | Degraded electrode or cracked ceramic gives a false residual flame signal | Electrode and lead replacement |
| Corroded or loose wiring harness | Occasional | Poor connection between PCB and gas valve delays the signal | Harness repair or replacement |
| Contaminated gas supply | Less common | Debris or oily residue from pipework or LPG affects valve seating | Valve clean or replacement, supply check |
Age is the strongest single predictor. We see F62 most often on ecoTEC Pro and ecoTEC Plus units installed roughly between 2011 and 2018. Those boilers are now eight to fifteen years old, which is squarely where gas valves and control boards start to give up.
Is F62 the same as F61, F28 or F29?
No, though they’re all part of the same gas and ignition family and they often appear in sequence. Knowing which one you’re looking at genuinely changes what the engineer packs in the van.
| Code | What the boiler is reporting | Most likely cause |
|---|---|---|
| F61 | Fault in gas valve actuation | PCB output stage, wiring, or gas valve coil |
| F62 | Delayed flame switch-off | Slow-closing gas valve, PCB, electrode |
| F27 | Flame simulation, flame detected when there shouldn’t be one | Faulty electrode, moisture, or PCB |
| F28 | Failure to ignite on start-up | No gas, gas valve, ignition unit, electrode |
| F29 | Flame goes out during operation | Gas supply interruption, flue recirculation, electrode |
If your boiler has cycled through F28 or F29 in recent months and has now landed on F62, mention that when you book the visit. A history of ignition faults points strongly at the electrode and lead, and that’s a much cheaper repair than a control board.
Can I fix an F62 fault myself?
No. There is nothing on the safe side of the casing that addresses this fault. Everything F62 points at, the gas valve, the PCB, the electrode and the harness, sits inside the boiler, and working on gas appliances without Gas Safe registration is both dangerous and illegal in Scotland, as it is across Great Britain.
There are four things you can safely do:
1. Write down the exact code. Take a photo of the display. If other codes appeared before this one, note those too.
2. Try one reset. Hold the reset button marked with a crossed-out flame for about three seconds, or turn the mode dial to the reset position, depending on your model. Check your manual. One reset only.
3. Check your other gas appliances. If your hob and gas fire also aren’t working, you may have a wider supply issue rather than a boiler fault, and that’s a different call to make.
4. If the fault returns, switch the boiler off at the fused spur or isolator and leave it off until an engineer attends.
Never remove the casing, touch the gas valve, PCB, electrodes or internal wiring, or keep resetting a boiler that keeps locking out.
If you smell gas
Leave the property. Turn the gas off at the meter only if it’s safe and on your way out. Once you’re outside, call the National Gas Emergency Service on 0800 111 999. Don’t use light switches, don’t use your phone indoors, and don’t go back in until you’re told it’s safe.
If you’re on LPG rather than mains gas, which covers a good number of rural properties across the Highlands, Borders and Argyll, that number doesn’t apply to you. Call your supplier’s emergency line instead. It’s on your tank or your last delivery note, so it’s worth finding it now rather than in a hurry.
What will a Gas Safe engineer actually do?
A proper F62 diagnosis follows a set order, and it takes longer than most fault-finding visits because gas work carries its own testing requirements.
- Gas tightness test on the installation before anything else.
- Working gas pressure check at the inlet and at the burner.
- Gas valve testing, including how quickly it closes on command.
- Ignition and flame monitoring electrode inspection, checking the tip, gap and ceramic insulator for cracks.
- PCB and wiring harness testing, including looking for condensate ingress and corroded connectors.
- Combustion analysis with a flue gas analyser after any repair, with the readings recorded.
That last step isn’t optional. Any work on the gas side of a Vaillant has to be signed off with combustion figures inside the manufacturer’s stated range. If an engineer offers to swap a part and leave without analysing the flue gases, get someone else.
How much does it cost to fix an F62 fault in Scotland?
Most F62 repairs land between £150 and £600, and the spread comes down to which of the three components has failed. Guide prices below are for Scotland in 2026, with parts fitted by a Gas Safe registered engineer.
| Repair | Guide cost (fitted) | Time on site | Notes |
|---|---|---|---|
| Diagnostic visit | £70–£130 | 45–90 mins | Often deducted from the repair if you proceed |
| Ignition electrode and lead | £140–£220 | 1–1.5 hours | The best outcome, and worth ruling in first |
| Wiring harness repair or replacement | £150–£300 | 1–2 hours | Depends on which loom |
| Gas valve replacement | £320–£550 | 2–3 hours | Includes combustion testing afterwards |
| PCB replacement | £350–£650 | 2–3 hours | Board needs configuring to your model |
| Vaillant fixed-price repair | From around £439 inc VAT | Varies | Confirm current pricing directly with Vaillant |
Two things affect the final figure more than anything else. Boiler age, because parts for pre-2015 ecoTEC models are getting harder to source and prices rise as availability falls. And whether more than one thing has failed, since a gas valve that’s been struggling can take the board with it.
Get the quote in writing before work starts, and ask specifically whether combustion testing and the parts guarantee are included.
Will my Vaillant warranty cover an F62 repair?
If the boiler is inside its guarantee period and your annual services are up to date, yes. Gas valves, PCBs and electrodes are all boiler components rather than system components, so they fall squarely inside what a Vaillant guarantee is meant to cover. Guarantees on the ecoTEC Plus range run up to 10 years when the boiler was installed by an approved installer and registered correctly.
The catch is servicing. A missed annual service invalidates most manufacturer guarantees, and F62 tends to show up on boilers old enough that at least one service has been skipped somewhere along the line. Dig out your service records before you call, because it changes who pays.
Is it worth repairing, or should I replace the boiler?
Repair makes sense if the boiler is under ten years old and the fault turns out to be the electrode or the wiring. Replacement usually makes more sense once you’re being quoted for a gas valve or a PCB on a boiler that’s twelve years old or more.
The arithmetic is straightforward. A PCB on a 2013 ecoTEC Pro might cost £500 fitted, which is a meaningful share of the price of a new A-rated boiler with a fresh ten-year guarantee. And it’s a repair to one ageing component in an appliance where the other ageing components haven’t failed yet. Fix the board today and there’s a fair chance you’re back on the phone about the fan or the gas valve inside two winters.
We’d never push a replacement on someone with a sound boiler and a cheap fault. But if you’re staring at a £600 quote on a fifteen-year-old unit, ask for a replacement price alongside it and compare properly.
How do I stop F62 happening again?
Servicing does most of the work here, because the failures behind F62 are wear-related and visible before they become lockouts.
- Book an annual service with a Gas Safe registered engineer. Electrodes get inspected and cleaned, gas pressures get checked, and combustion gets tested. Worn parts get spotted early.
- Keep the condensate trap and pipe clear. A blocked or leaking trap is how moisture reaches the PCB. In Scotland this matters twice over, because condensate pipes run externally in a lot of properties and freeze during a cold snap.
- Lag any external condensate pipework. Cheap to do, and it prevents a chain of problems every January.
- Deal with ignition faults straight away. Recurring F28 or F29 codes are the electrode telling you it’s on the way out. Sorting a £180 electrode is much better than waiting for it to take a control board with it.
- Keep your service records. They’re what protects your guarantee.
The bottom line
F62 is a gas safety lockout caused by delayed flame switch-off, and the boiler is doing exactly the right thing by refusing to run. Note the code, reset once, and if it returns, switch the boiler off and get a Gas Safe registered engineer out. Don’t open the casing, don’t keep resetting it, and don’t let anyone without the right qualifications near it.
Need an engineer? Edinburgh Boiler Company covers Edinburgh, the Lothians and central Scotland with Gas Safe registered, Vaillant-approved engineers, full combustion testing on every gas repair, and clear written pricing before any work starts. Get in touch and we’ll get it diagnosed properly.
This guide is general advice. Always refer to your specific Vaillant model’s user manual for reset instructions, and never remove the boiler casing. Gas work must be carried out by a Gas Safe registered engineer. If you smell gas, leave the property and call 0800 111 999, or your LPG supplier’s emergency line if you’re off the mains gas grid.
