The Vaillant F62 error code means the boiler detected the flame going out later than it should after the gas valve was told to close. Vaillant treats this as a gas valve shut off fault, so the boiler locks out to stay safe, and the cause almost always needs a Gas Safe registered engineer.
Quick answer: F62 on a Vaillant boiler means the flame switch-off was detected after a delay. Vaillant lists a defective gas valve, PCB or ignition electrode as causes. You may press reset once to see if it clears, but if F62 returns, stop and call a Gas Safe registered engineer. Never open the casing yourself.
What Does the Vaillant F62 Error Code Mean?
F62 means the flame did not go out on time when the boiler shut the gas off.
Vaillant’s UK boiler fault codes list describes F62 as “The flame switch-off was detected after a delay.” When a burner finishes, the control board closes the gas valve and expects the flame sensor to lose its signal almost at once. If the flame signal lingers, the board cannot be sure the gas valve has closed fully, so it locks out.
The installation manuals use slightly different names for the same code. The HOME combi manual calls F.62 “Gas valve switch-off control”, and the older ecoTEC plus manual calls it “Gas valve switch-off delay”. Some websites say F62 means the gas valve failed to open. That is not how Vaillant describes it: a failure to light is F28.
What Causes the F62 Error?
Vaillant’s own lists point to three parts inside the boiler, all of them engineer work.
- Defective gas valve: the valve closes slowly or not completely. The HOME combi manual lists “gas valve leaking” and “delayed switch-off of gas valve” as possible causes.
- Defective PCB: the main control board misreads the flame signal or the valve command. The manual also lists “electronics defective”.
- Defective ignition electrode: Vaillant’s UK page names it, and the manual lists “delayed extinguishing of flame signal”. A worn or contaminated electrode can keep reporting a flame after it has gone.
Unlike F22 (low pressure) or a frozen condensate pipe, none of these causes sits outside the casing, which is why Vaillant says “This is a case for an expert” for F62.
How Do You Fix the F62 Error Yourself?
There is no homeowner repair for F62. What you can do safely is check, reset once and record what happens.
- Check for a gas smell. If you smell gas, do not reset. Follow the gas emergency steps below.
- Note the code and the time. Write down F62, any other codes shown, and whether it happened when heating or hot water switched off.
- Press reset once. Vaillant’s operating instructions say to hold the reset button for longer than three seconds. Their limit of three attempts is for ignition problems; for F62 one attempt is enough to tell whether it was a one off.
- Watch the next few cycles. If the boiler runs normally, keep an eye on it and mention the event at the next service.
- If F62 returns, leave it locked out and book a Gas Safe registered engineer.
Safety: Stop if F62 comes back after one reset. Do not keep resetting, remove the casing, or touch the gas valve, electrode or PCB. HSE says anyone employed to work on gas appliances in a home must be a Gas Safe registered engineer. If you smell gas, open doors and windows, avoid switches and naked flames, leave the building and call the National Gas Emergency Service on 0800 111 999.
When Should You Call an Engineer?
Call a Gas Safe registered engineer as soon as F62 shows a second time. Because the manual includes a leaking gas valve among the possible causes, this is not a code to live with. The Health and Safety Executive makes clear that only a Gas Safe registered engineer may work on domestic gas appliances.
If your boiler is under guarantee, contact Vaillant’s customer service or your installer first, as Vaillant’s fault code page directs. Have the model name, the codes you saw and your service record ready.
F62 Compared With Other Vaillant Flame Codes
Vaillant uses several codes for gas, flame and gas valve problems. The meanings below are Vaillant’s own, from its UK fault code page and installation manuals.
| Code | Vaillant meaning | Causes Vaillant lists | Who fixes it |
|---|---|---|---|
| F27 | Flame signal detected while the burner is off | Fault in flame detection | Gas Safe engineer |
| F28 | Flame signal not detected during ignition | Gas isolator closed, low gas pressure, ignition parts | Homeowner checks isolator, then engineer |
| F29 | Re-ignition after flame loss unsuccessful | Gas supply interrupted, flue, condensate, ignition parts | Engineer if it returns |
| F61 | Gas valve control fault | Gas valve wiring, gas valve, PCB | Gas Safe engineer |
| F62 | Flame switch-off detected after a delay | Gas valve, PCB, ignition electrode | Gas Safe engineer |
| F63 | EEPROM fault | Electronics defective | Gas Safe engineer |
If your Vaillant is showing a pressure fault such as F22 rather than F62, our guide on how to repressurise a combi boiler covers the filling loop, which is a safe homeowner job.
How Can You Stop the F62 Error Coming Back?
F62 is caused by wear in parts you cannot reach, so prevention comes down to maintenance and early action.
- Book an annual service. HSE advises that gas appliances are serviced at least once a year by a Gas Safe registered engineer. It gives an engineer the chance to spot wear before it causes a lockout.
- Keep the guarantee valid. Vaillant’s operating instructions for the HOME combi say an annual service by a competent person is needed for the second year of the guarantee to be valid. Check your own guarantee terms.
- Report one off lockouts. Mention any F62 that cleared after a reset at the next service, so the engineer can test the gas valve.
- Plan ahead for an older boiler. If an ageing boiler keeps needing gas valve and PCB parts, the boiler size calculator gives a guide kW range to compare replacement quotes, and the gas bill calculator helps you track running costs.
Vaillant F62 Error Code FAQs
What does F62 mean on a Vaillant boiler?
Vaillant says F62 means the flame switch-off was detected after a delay. When the gas valve closed, the flame signal took too long to disappear, so the boiler locked out because it could not confirm the valve had shut.
Can I reset a Vaillant boiler with F62?
You can press reset once, holding it for longer than three seconds as Vaillant’s instructions describe. If F62 comes back, do not keep resetting. Call a Gas Safe registered engineer, because the causes are inside the boiler.
Is the F62 fault dangerous?
The lockout is a safety feature, so the boiler is protecting you. Vaillant’s manual lists a leaking gas valve as a possible cause, so treat it seriously. If you smell gas, leave the building and call 0800 111 999.
What is the difference between F61 and F62?
F61 is a gas valve control fault, which Vaillant links to the gas valve wiring, a defective gas valve or the electronics. F62 is about timing: the flame went out later than expected after the valve was told to close. Both need a Gas Safe registered engineer.
Will a faulty gas valve always cause F62?
No. Vaillant also lists the PCB and the ignition electrode as causes of F62, and a gas valve problem can show as other codes such as F61. Only an engineer’s tests can confirm which part has failed.
Does F62 mean I need a new boiler?
Not necessarily. The gas valve, PCB and electrode are replaceable parts. Whether repair is worthwhile depends on the boiler’s age and condition, so ask the engineer for a written diagnosis before deciding.
Checked October 2026. Sources: Vaillant UK, Boiler fault codes list, Vaillant HOME combi installation and maintenance instructions, Vaillant HOME combi operating instructions, Vaillant ecoTEC plus operating instructions, HSE, Domestic gas: frequently asked questions.
