F62 is a gas-side fault, so leave the boiler switched off and book a Gas Safe registered engineer. Vaillant’s own advice on the code is blunt: “This is a case for a Vaillant engineer. Don’t try to solve it yourself as opening the boiler casing can be dangerous.” If you can smell gas, do not touch electrical switches, open the doors and windows, turn the gas off at the meter control handle unless the meter is in a cellar, leave the property and ring the National Gas Emergency Service on 0800 111 999.
This page is the money-and-decision side of the code: what the repair involves, what it costs against published prices, whether it is worth paying for, and how annual servicing lowers the risk of it coming back. For the step-by-step diagnostics, read our Vaillant F62 fault code guide.
What does the Vaillant F62 fault code mean?
Vaillant UK publishes F62 in its own boiler fault-code list, where the code is written with a dot as F.62 and defined in one line.
| Code | Vaillant’s wording | Vaillant’s listed causes |
|---|---|---|
| F.62 | “The flame switch-off was detected after a delay.” | “Gas valve defective. PCB defective. Ignition electrode defective.” |
In plain English: your boiler does not simply switch the burner off and walk away, it watches the flame die. The control board tells the gas valve to close, the ignition electrode reports that the flame has gone, and the boiler expects those two events within a set window. A flame still detected after that window means gas may still be reaching the burner, so the boiler shuts down. F62 is that shutdown.
Two things follow before you spend money. F62 is a timing complaint about the boiler’s own combustion chamber, not proof that gas is escaping into your home. And the code cannot say which of the three parts is at fault, so a quote given down the phone is guesswork.
What causes an F62, and what the engineer checks
Vaillant names three suspects. A competent engineer works through all three rather than swapping the most expensive one first.
A defective gas valve
The gas valve meters gas to the burner and closes it on command from the control board. If it is slow to close, closes only partly, or leaks past its seat, gas keeps reaching the burner a fraction of a second longer than the boiler allows, and the flame lingers. That is the classic F62 picture.
A defective PCB
The printed circuit board decides when the valve opens and closes, and reads the flame signal coming back. A failing output, a dry joint or a damaged connector can send the close instruction late, or misread a good flame signal as a late one. Either produces F62 with a gas valve that turns out to be fine.
A defective ignition electrode
This one is on Vaillant’s own list and most F62 write-ups leave it out. The electrode sparks the burner alight, then senses that the flame is present. A dirty, cracked or wrongly gapped electrode can keep reporting a flame that has already gone out, which the boiler reads as a switch-off delay even though the gas valve closed on time. It is usually the cheapest of the three to put right, so it deserves testing before anyone quotes for a control board.
The lockout is deliberate. One reset following your manual is reasonable, because Vaillant accepts that resetting “can resolve a fault or temporarily get your boiler working again”. If F62 comes back, it is hardware, and the Health and Safety Executive is clear that work inside a gas appliance is for a Gas Safe registered engineer.
What does it cost to fix a Vaillant F62?
The one price we can point at with a source is Vaillant’s own. Vaillant UK advertises a fixed-price one-off boiler repair “From £439 one-off payment (inc. VAT) payable at point of booking” (Vaillant UK, price checked August 2026). Vaillant says that job includes “a gas safety check”, that “all parts fitted are guaranteed for 12 months, exclusions apply”, and that “labour is covered for 90 days”.
That is a starting price, not an F62-specific quote. An independent Gas Safe registered engineer usually prices as a call-out charge plus the part. The only number that decides anything is your own written quote, so make it comparable:
- Ask for the parts figure and the labour figure separately, in writing, before work starts.
- Ask what was tested to land on that part, given Vaillant lists three possible causes.
- Ask what guarantee comes with the repair. Vaillant’s own fixed-price job carries 12 months on parts fitted and 90 days on labour, a fair benchmark for any quote.
Before you pay anything, check whether your boiler is still inside its manufacturer guarantee. Vaillant’s covers “material and labour charges to repair or replace components within the boiler against manufacturing defects”, the category a gas valve, control board or ignition electrode falls into, so an F62 repair can cost you nothing. Our guide to checking your Vaillant boiler warranty shows how to confirm it.
Is an F62 worth repairing?
Usually yes. F62 points at components rather than at the boiler’s heart: a gas valve, a control board and an ignition electrode are all replaceable parts in an otherwise sound appliance. The sums change when several of these are true at once: the boiler is well past its guarantee, the quote is a large fraction of a replacement, parts are hard to source, and it is not the first breakdown of the year. Our guide on whether to repair or replace a boiler sets out that comparison.
How to lower the risk of F62 coming back
You cannot service a gas valve yourself, and you should not try. What you can do is have someone qualified look at these parts once a year, before they fail. A service is not a guarantee against F62, because a gas valve or a control board can fail without warning. Vaillant’s advice is direct: “To maximise the performance and reliability of your boiler, ensure it is serviced once a year by a Gas Safe registered engineer.” Vaillant lists the benefits as keeping the boiler “running safely and efficiently”, maintaining your guarantee and avoiding “future repairs when problems are identified early”. Its own annual service is advertised “from £139 (price inc VAT)” (Vaillant UK, price checked August 2026).
Vaillant describes the service work as including “combustion analysis, gas safety inspections, hydraulic assessments, electrical system evaluations, performance testing, and water quality analysis”, along with cleaning of ignition components. Those are the checks most likely to pick up a weak flame signal or a dirty electrode before it turns into a lockout in December.
There is a second reason not to skip it. Vaillant’s guarantee terms require that “the boiler must be serviced annually by a Vaillant or other registered Gas Safe Registered engineer”, and that “service details must be recorded in the Benchmark logbook which must be available for inspection”. The boiler must also be registered within 30 days of installation, or the guarantee “will revert to 12 months from date of installation”.
What to do right now if you see F62
- If you can smell gas, stop and treat it as an emergency. Do not smoke or light matches, do not turn electrical switches on or off, open doors and windows, turn off the meter at the control handle unless the meter is in a cellar, and ring the National Gas Emergency Service on 0800 111 999. That line is free and staffed 24 hours a day. It is a national emergency line, not a Smart Plan number.
- Check your other gas appliances. If the hob and fire work normally, the problem is the boiler rather than your gas supply, which the engineer will want to know.
- Reset once, following your Vaillant manual. Vaillant accepts that a reset sometimes clears a fault or gets a boiler going temporarily. Once is the limit.
- Do not open the casing. Vaillant advises against it and the work behind it is legally restricted to Gas Safe registered engineers.
- Check your guarantee before you book. Two minutes here can be the difference between a free repair and a bill.
- Book a Gas Safe registered engineer and ask them to test the gas valve, the PCB and the ignition electrode, not just the first of the three. You can request a callback from us and we will call you back, or see our full Vaillant fault code list if other codes appeared too.
Other questions people ask about F62
Is it safe to use the boiler while F62 is showing?
The boiler has already decided for you: it locks out rather than run. Leave it switched off until an engineer has tested it. F62 on its own is not evidence of gas escaping into your home, but a leaking gas valve is on Vaillant’s list of causes, which is why the smell-of-gas steps above matter.
Is F62 the same as F28?
No. Vaillant defines F28 as “the flame signal was not detected during the ignition phase”, so the boiler never lights. F62 is a boiler that does light and then fails to shut down cleanly. They share two suspects, the PCB and the ignition electrode.
Will my Vaillant guarantee pay for an F62 repair?
It can, if the guarantee is live and its conditions were met: it covers repairing or replacing components inside the boiler against manufacturing defects. It will not help if the boiler was never registered within 30 days, if annual services were skipped, or if the Benchmark logbook cannot be produced.
Where Smart Plan fits
Smart Plan is a service plan from UK Boiler Company Ltd, not insurance. Add the boiler and central heating module and covered repairs are arranged through a national network of thousands of Gas Safe registered engineers, with parts and labour paid up to £500 in a 12-month period if your boiler is under seven years old, or £200 if it is over seven. We aim to get an engineer out to you within two working days; cover-plan call-outs run Monday to Friday, 08:00 to 18:00 unless it is a genuine emergency breakdown. A £95 call-out fee, paid in advance, applies in your first 30 days, for issues the plan does not cover, where the engineer cannot get access, and for early annual-service requests. Cover still applies during those first 30 days. A cover plan is for future breakdowns: under the terms, a fault already in existence when your agreement starts is a defect, and works to repair a defect we identify are excluded, so we would quote for that repair separately. Using any service starts a 12-month agreement period, and leaving early after that costs the remaining months or 75% of the outstanding balance. There is a 14-day cooling-off period, which ends once a service is carried out.
Get your boiler looked at.
Tell us what your boiler is showing and we will call you back to talk through your options and, if you want us to, arrange a Gas Safe registered engineer. Repair work is chargeable unless it is covered by your Vaillant guarantee or a Smart Plan cover plan. An annual service by a Gas Safe registered engineer is also one of Vaillant’s own conditions for keeping your guarantee valid, alongside registering the boiler within 30 days and keeping the Benchmark logbook up to date.
Sources (Vaillant pages and prices checked August 2026): Vaillant UK boiler fault codes · Vaillant UK boiler repair · Vaillant UK boiler service · Vaillant domestic boiler guarantee terms · HSE domestic gas FAQs · National Gas emergency contacts
