F.62
Vaillant Boiler
Severity: ModerateWhat Does This Error Mean?
Vaillant F.62 means the gas valve did not close within the expected time after the burner was commanded off.
The PCB watches for flame extinction within a few seconds — if the flame lingers, F.62 latches.
Cause is usually a sticking gas valve, but a slow flame rod or a contaminated burner can also delay flame extinction.
This is a Gas Safe engineer job, not a DIY fix.
Affected Models
- Vaillant ecoTEC Plus
- Vaillant ecoTEC Pro
- Vaillant ecoFIT Pure
- Vaillant ecoFIT Sustain
Common Causes
- Gas valve internals sticking after years of use
- Burner clogged with combustion residue holding flame
- Flame rod slow to report flame loss
- PCB flame-sense input timing drifting
- Gas pressure too high (regulator issue) sustaining flame longer
How to Fix It
-
Reset once.
Press the reset button on the front of the boiler.
If F.62 was a one-off glitch, reset clears it.
If F.62 returns within hours or on the next heat call, repair is needed. -
Stop using the boiler if it returns.
F.62 indicates gas behaviour outside spec.
Repeated resets without finding the cause is not safe.
Switch off at the spur and call a Gas Safe engineer. -
Engineer step: clean the burner.
Combustion residue on the burner surface keeps the flame burning slightly longer than expected.
Removing and brushing the burner often restores normal flame-out timing without parts replacement. -
Engineer step: check gas valve closure.
Engineer connects a manometer to the test point.
Commands the valve closed and watches for residual pressure or flow.
A valve that closes slowly or incompletely is the typical fault. -
Engineer step: replace the gas valve.
If the valve is sticking, replacement is the fix.
Vaillant gas valves are 200-400 GBP plus labour.
This is not a part to buy aftermarket — only Vaillant or properly-matched OEM equivalents are gas-safe in this application. -
Engineer step: gas pressure check.
After valve replacement, the engineer measures inlet and burner pressures against the data plate.
Adjustments to the regulator may be needed to bring readings into spec. -
Final test.
After repair, the engineer cycles the boiler several times — heat call, hot water call, idle.
Each shutdown should produce immediate flame extinction.
No F.62 across multiple cycles confirms the repair.
Frequently Asked Questions
Is F.62 dangerous?
The boiler locks out when F.62 latches, so there is no continuous unsafe operation.
The risk is only present if the alarm is repeatedly bypassed.
Leave the boiler off and let an engineer fix it properly.