F0 Boiler Fault Code: What It Means on Every Brand

The F0 fault code appears on 3 brands — Protherm, Viessmann and Worcester Bosch — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

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 F0 means	Severity	DIY?
PProthermshown as F.0	The F.0 fault code (also shown as F0) on Protherm boilers indicates that the heating circuit water pressure has dropped below the minimum acceptable threshold — typically under 0.6 bar. Full guide →	Lockout — engineer likely	Some checks
VViessmann	The F0 fault code on most Viessmann Vitodens boilers (including the popular 100-W and 050-W) indicates that the boiler has detected dangerously high temperatures and shut itself down as a… Full guide →	Lockout — engineer likely	Some checks
WBWorcester Bosch	The F0 fault code signals that your Worcester Bosch boiler has detected a serious internal error and has stopped normal operation to protect itself. Full guide →	Lockout — engineer likely	No

F0 brand by brand

Protherm F.0

The F.0 fault code (also shown as F0) on Protherm boilers indicates that the heating circuit water pressure has dropped below the minimum acceptable threshold — typically under 0.6 bar. When this happens, the boiler shuts itself down as a safety measure and the LED beneath the pressure symbol flashes on the display. The letter F will flash on the screen alongside the error number. The boiler will not fire again until the pressure is restored to a safe level, normally between 1 and 1.5 bar. This code appears across the Protherm range including the Tiger and Leopard/Kombi series.

Causes, fixes & costs for Protherm F.0 → · All Protherm codes

Viessmann F0

The F0 fault code on most Viessmann Vitodens boilers (including the popular 100-W and 050-W) indicates that the boiler has detected dangerously high temperatures and shut itself down as a safety precaution. This is a volatile lockout, meaning the boiler will not restart until you manually reset it. On certain Vitodens controller variants the same code can instead point to a flow temperature sensor fault — where the sensor reports unrealistically high or low readings — so if the steps below don't resolve the issue, that possibility should be investigated by an engineer. Because the code meaning can vary by model, always confirm against your specific boiler's documentation or speak to a Viessmann-trained installer.

Causes, fixes & costs for Viessmann F0 → · All Viessmann codes

Worcester Bosch F0

The F0 fault code signals that your Worcester Bosch boiler has detected a serious internal error and has stopped normal operation to protect itself. The boiler's fault indicator LED and reset button will typically flash red. F0 is a broad category code — your display will usually show a sub-code alongside it (for example, F0 238) that pinpoints which component has triggered the lockout. The most commonly seen sub-code is F0 238, which points specifically to a gas valve or control box fault. Other F0 sub-codes can relate to PCB failures, wiring problems, or in some Greenstar models, a pressure sensor issue. When the boiler locks out on F0, you will lose heating, hot water, or both until the underlying fault is resolved.

Causes, fixes & costs for Worcester Bosch F0 → · All Worcester Bosch codes

Frequently asked questions

Is the F0 fault code the same on every boiler?

No. F0 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a F0 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a F0 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.