F.32 Boiler Fault Code: What It Means on Every Brand

The F.32 fault code appears on 5 boiler brands — Glow-worm, Heatline, Protherm, Saunier Duval and Vaillant — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

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.32 means	Severity	DIY?
GWGlow-wormshown as F32	The F32 fault code on a Glow Worm boiler signals that the fan is not maintaining a consistent or adequate speed. Full guide →	Lockout — engineer likely	No
HHeatlineshown as F32	The F32 fault code on Heatline boilers (including the Capriz range) signals that the boiler's control board has detected an issue with fan operation — most commonly that the fan is running… Full guide →	Lockout — engineer likely	No
PProtherm	The F.32 code appears on Protherm boilers when the ventilator (fan) is detected running outside its acceptable speed range. Full guide →	Lockout — engineer likely	No
SDSaunier Duval	The F.32 fault code indicates that your Saunier Duval boiler has detected a problem with the combustion fan or flue gas evacuation. Full guide →	Lockout — engineer likely	No
VVaillant	The F.32 fault code on a Vaillant ecoTEC boiler indicates that the fan is not running at the correct speed or is behaving erratically. Full guide →	Lockout — engineer likely	No

F.32 brand by brand

Glow-worm F32

The F32 fault code on a Glow Worm boiler signals that the fan is not maintaining a consistent or adequate speed. Because the fan is responsible for pushing waste combustion gases safely out through the flue, any significant variation in its speed triggers an automatic lockout — the boiler shuts down as a precaution to prevent dangerous gases from remaining inside the appliance or being expelled incorrectly. You will lose both heating and hot water until the underlying issue is resolved. This fault is closely related to the same fan-speed monitoring technology used across the wider Vaillant Group range, of which Glow Worm has been a part since 2001.

Causes, fixes & costs for Glow-worm F32 → · All Glow-worm codes

Heatline F32

The F32 fault code on Heatline boilers (including the Capriz range) signals that the boiler's control board has detected an issue with fan operation — most commonly that the fan is running at the wrong speed or receiving insufficient voltage (typically around 4V rather than the required level). Because the fan is responsible for pushing waste combustion gases safely out through the flue, the boiler immediately locks out as a precaution to prevent dangerous gases building up inside the appliance. You'll lose both heating and hot water until the fault is cleared. Some owners also notice a low humming noise from the boiler when this code appears. As Heatline is part of the Vaillant Group and shares the same technology platform, the F32 on a Heatline Capriz is directly equivalent to the Vaillant F32 fault.

Causes, fixes & costs for Heatline F32 → · All Heatline codes

Protherm F.32

The F.32 code appears on Protherm boilers when the ventilator (fan) is detected running outside its acceptable speed range. In other words, the boiler's control system has measured the fan spinning either too slowly or erratically, and has shut the boiler down as a precaution. Because the fan is responsible for pushing waste combustion gases safely out through the flue, the boiler will not attempt to ignite again until this fault is resolved — this is a deliberate safety lockout. In some cases the code can also be triggered when the anti-freeze protection function becomes active alongside an air-circulation problem.

Causes, fixes & costs for Protherm F.32 → · All Protherm codes

Saunier Duval F.32

The F.32 fault code indicates that your Saunier Duval boiler has detected a problem with the combustion fan or flue gas evacuation. The fan is responsible for two critical jobs: drawing fresh air into the burner and pushing potentially dangerous flue gases safely out of your home. When the boiler's control board detects that the fan isn't running at the correct speed — or that there is insufficient draught through the flue — it locks out and displays F.32 as a safety precaution. Because poorly evacuated flue gases carry a real risk of carbon monoxide entering your home, the boiler will not restart until the underlying fault is resolved. If you see F.32, switch off the boiler, ventilate the room, and do not attempt to override the lockout.

Causes, fixes & costs for Saunier Duval F.32 → · All Saunier Duval codes

Vaillant F.32

The F.32 fault code on a Vaillant ecoTEC boiler indicates that the fan is not running at the correct speed or is behaving erratically. The fan has two critical jobs: drawing fresh air into the combustion chamber and pushing waste flue gases safely out of your home. When the boiler's control system detects that the fan speed is outside acceptable limits — either too slow, too fast, or inconsistent — it triggers a protective lockout to prevent incomplete combustion and the potential build-up of carbon monoxide. The boiler will stop providing heating and hot water until the fault is resolved. You may also notice a humming sound from the boiler before or during the lockout.

Causes, fixes & costs for Vaillant F.32 → · All Vaillant codes

Frequently asked questions

Is the F.32 fault code the same on every boiler?

Broadly, yes — on Glow-worm, Heatline, Protherm, Saunier Duval and Vaillant the F.32 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.32 fault myself?

Not usually. On every brand listed, F.32 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.32 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.