F.62 Boiler Fault Code: What It Means on Every Brand

F62 concerns the gas valve closing correctly on most brands that use it (Vaillant, Saunier Duval, Protherm, Heatline — a 'delayed flame switch-off'), which is a combustion-safety fault the boiler treats seriously. Glow-worm uses F62 for a main board fault. Either way it is engineer-only; one reset at most.

Lockout — engineer likely 5 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What F.62 means	Severity	DIY?
GWGlow-wormshown as F62	The F62 code on a Glow-Worm boiler signals an electronic fault on the main control board (PCB). Full guide →	Lockout — engineer likely	No
HHeatlineshown as F62	The F62 fault code on Heatline boilers signals that a delayed flame switch-off has been detected. Full guide →	Lockout — engineer likely	No
PProtherm	The F.62 code on a Protherm boiler indicates that the gas valve has not closed within the expected timeframe after the burner shuts down. Full guide →	Lockout — engineer likely	No
SDSaunier Duval	The F.62 code appears when your Saunier Duval boiler detects that the gas valve has not closed correctly. Full guide →	Lockout — engineer likely	No
VVaillant	The F.62 code is a combustion safety fault. Full guide →	Lockout — engineer likely	No

F.62 brand by brand

Glow-worm F62

The F62 code on a Glow-Worm boiler signals an electronic fault on the main control board (PCB). The PCB acts as the boiler's central processor — it coordinates every component from the gas valve to the pump — so when it develops a fault the boiler will lock out and stop providing heating or hot water. F62 sits within a family of related electronic fault codes (F61 through F67) that all point to main board issues of varying types; F62 specifically indicates a detected fault within the board's own circuitry or its communication with connected components. Because the root cause is not always a dead PCB — faulty sensors or damaged wiring can trigger the same code — a proper diagnosis by a Gas Safe registered engineer is essential before any parts are replaced.

Causes, fixes & costs for Glow-worm F62 → · All Glow-worm codes

Heatline F62

The F62 fault code on Heatline boilers signals that a delayed flame switch-off has been detected. In plain terms, the boiler's control system has noticed that the gas valve is taking too long to close after the burner should have shut down. Because uncontrolled gas flow is a potential safety hazard, the boiler immediately locks itself out and will not restart until the underlying fault has been resolved. This is one of the more serious fault codes in the Heatline range and always warrants attention from a Gas Safe registered engineer — do not ignore it or attempt repeated resets.

Causes, fixes & costs for Heatline F62 → · All Heatline codes

Protherm F.62

The F.62 code on a Protherm boiler indicates that the gas valve has not closed within the expected timeframe after the burner shuts down. In plain terms, the boiler's control system detected a delay in flame extinction — meaning gas continued to flow (or was detected as flowing) for longer than it should after a shutdown signal was issued. Because this represents a potential gas safety risk, the boiler enters lockout mode and stops operating until the fault is investigated and cleared. Protherm shares its underlying platform with Vaillant, so F.62 carries the same meaning and follows the same diagnostic path on both brands.

Causes, fixes & costs for Protherm F.62 → · All Protherm codes

Saunier Duval F.62

The F.62 code appears when your Saunier Duval boiler detects that the gas valve has not closed correctly. Rather than continuing to operate in an unpredictable state, the boiler triggers a safety lockout and shuts down completely — stopping both heating and hot water. Because this fault relates directly to gas flow control, it is treated as a serious safety issue and should not be left unattended. The display will flash and alternate between the fault digits to draw your attention. A single reset attempt is reasonable, but if F.62 returns immediately or persistently, a Gas Safe registered engineer must investigate before you use the boiler again.

Causes, fixes & costs for Saunier Duval F.62 → · All Saunier Duval codes

Vaillant F.62

The F.62 code is a combustion safety fault. It appears when your Vaillant boiler detects that the flame has switched off too slowly after the burner should have stopped — in practice, the gas valve is taking longer than it should to close. Because this involves the supply of gas to the burner, the boiler treats it as a potentially hazardous situation and locks out automatically to protect you. This is a fault that always requires investigation by a Gas Safe registered engineer; it is not something a homeowner can repair.

Causes, fixes & costs for Vaillant F.62 → · All Vaillant codes

Frequently asked questions

Is the F.62 fault code the same on every boiler?

Broadly, yes — on Glow-worm, Heatline, Protherm, Saunier Duval and Vaillant the F.62 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a F.62 fault myself?

Not usually. On every brand listed, F.62 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a F.62 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.