Boiler fault codes
Vaillant F62 Fault Code: The Flame Went Out Too Slowly
Published
Vaillant display
F62
What it means
F.62 means that when the boiler told the gas valve to close, the flame took too long to go out. The boiler reads that as a gas valve that may not be shutting off cleanly, and locks out.
Safe to check yourself
- Press the reset button once, then watch whether the boiler runs and shuts down normally
- Check for a gas smell around the boiler and meter before and after the reset
- Check the carbon monoxide alarm near the boiler is working and not sounding
- Write down whether F.62 appears at the end of a heating run, after hot water use or at random
Call an engineer if
- F.62 returns after one reset
- The burner can be heard or seen still running after the heating or tap is turned off
- The CO alarm sounds, or anyone in the house has headaches, dizziness or nausea near the boiler
- You smell gas: open windows, turn off at the meter if it is safe, do not use switches, leave the property and call 0800 111 999 first
A Vaillant F62 fault means the boiler detected a flame for longer than it should after telling the gas valve to close. Vaillant's manual calls it a gas valve switch-off delay. It points to a gas valve that is not sealing, a faulty control board or a flame sensing fault. Reset once; if it returns, call a Gas Safe engineer.
What does F62 actually mean on a Vaillant?
Every time your boiler finishes a run it closes the gas valve and expects the flame sensor to see the flame die within a set moment. If the flame is still being sensed after that, the boiler cannot be sure the gas has actually stopped, so it shows F.62 and refuses to light again until it is reset.
The two Vaillant sources describe it in slightly different words. The ecoTEC plus 937 installation manual calls F.62 a switch-off delay of the gas valve and gives the causes as a leaking gas valve or defective electronics. Vaillant's online fault code list describes it as the flame switch-off being detected after a delay, and adds the ignition electrode as a possible cause alongside the gas valve and the PCB. The meaning is the same; the online list simply names one more part to test.
Is F62 dangerous?
It is a safety lockout, which means the boiler has done its job and stopped. The concern behind the code is a gas valve that lets gas through when it should be shut. That is why F.62 is not a code to reset over and over to get the heating back for a few hours.
Reset once. If the boiler then runs and switches off normally and the code does not come back, it may have been a one-off. If F.62 returns, switch the boiler off at the fused spur and leave it off. Keep the room ventilated and make sure your carbon monoxide alarm works; our page on carbon monoxide signs from a boiler lists what to watch for.
If you smell gas at any point, open windows, turn the gas off at the meter if you can do so safely (not if it is in a cellar), do not operate switches, then leave the property and call the National Gas Emergency Service on 0800 111 999. Our guide on what to do if you smell gas goes through it step by step.
Which parts cause F62, in the order an engineer tests them
The engineer will not start by swapping the gas valve, because it and the PCB are the two dearest parts on the list. A sensible diagnostic order looks like this:
- Ignition and flame sensing electrode: checked for carbon build-up, a worn tip or a cracked ceramic, which can make the board read flame signal after the flame has gone
- Electrode lead and earth connections: a poor earth can give a false flame reading
- Gas valve: a let-by test with a manometer to prove whether gas passes when the valve is closed
- Control board (PCB): suspected once the electrode, wiring and valve all test sound
What an F62 repair typically involves
An electrode is a small, inexpensive part and is often replaced during a service anyway. A genuine gas valve for an ecoTEC plus usually costs roughly £150 to £350 as a part from trade suppliers, plus labour, and after fitting the engineer must carry out a gas tightness test and a combustion check. A replacement PCB tends to sit at the top of the range. Any of these jobs involves work on gas, which under the Gas Safety (Installation and Use) Regulations 1998 is for a Gas Safe registered engineer only.
Our Vaillant boiler repair service runs 24/7 across London and everywhere inside the M25 for a £60 call-out, and the repair price is agreed with you on site before any work starts. Gas work is carried out by Gas Safe registered engineers.
If the boiler is showing more than one code, compare it with F61, a gas valve control fault, and F28, a failure to ignite. Together they help narrow down whether the valve, the electrode or the board is at fault.
Questions people ask
Can I keep resetting my Vaillant on F62 to get heating back?
No. One reset is reasonable. Because F.62 points at a gas valve that may not be closing properly, repeated resets keep putting that valve back into service. Leave it off after the second appearance.
What is an F62 boiler fault on other brands?
Fault numbers are specific to each manufacturer, so an F62 on another make can mean something quite different. This page covers Vaillant only; check your own boiler's manual or our Vaillant fault code list to confirm the make.
Does F62 mean I need a new boiler?
Rarely. The usual fixes are an electrode, a gas valve or a control board, all of which are standard spare parts for ecoTEC boilers. Replacement only comes into the conversation when the boiler is old and the valve and board both need replacing.