F08 Boiler Fault Code: What It Means on Every Brand

The F08 fault code appears on 2 brands — Ferroli and Protherm — 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 2 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 F08 means	Severity	DIY?
FFerroli	The F08 code on a Ferroli boiler means the overtemperature protection circuit has triggered because the heating water in the heat exchanger has reached an excessively high temperature —… Full guide →	Engineer may be needed	Some checks
PProthermshown as F.08	The F.08 code appears on Protherm boilers — including the Gepard, Panther, Puma Condens, Lynx Condens, and Medved Condens ranges — when the control board detects an earthing or grounding… Full guide →	Lockout — engineer likely	No

F08 brand by brand

Ferroli F08

The F08 code on a Ferroli boiler means the overtemperature protection circuit has triggered because the heating water in the heat exchanger has reached an excessively high temperature — specifically, if the water temperature hits 100°C or above and stays there for five or more seconds, the boiler logs this event. F08 is classified as a blocking fault, which means it is recorded in the boiler's event register but does not necessarily stop the boiler from running immediately. However, if the underlying problem is not addressed and F08 occurs repeatedly, it can escalate into a full lockout displayed as A08 (or A03 in some circumstances). The companion code A08 is the lockout version of the same fault and requires a manual reset to clear. Both codes point to the same root cause: the heat exchanger is getting too hot, usually because water is not circulating properly around the system.

Causes, fixes & costs for Ferroli F08 → · All Ferroli codes

Protherm F.08

The F.08 code appears on Protherm boilers — including the Gepard, Panther, Puma Condens, Lynx Condens, and Medved Condens ranges — when the control board detects an earthing or grounding fault associated with the domestic hot water (DHW) heater circuit or its linked NTC temperature sensor. Protherm uses a shared error-numbering system across its wall-hung and floor-standing boiler families, so F.08 carries the same meaning throughout the range. In practical terms, the board has received a signal from the DHW heater sensor circuit that is absent, out of range, or looks electrically abnormal — typically pointing to a wiring-to-earth fault, a short circuit, or a degraded sensor. The boiler locks out as a safety precaution until the underlying electrical fault is resolved. F.08 sits within the F.00–F.09 sensor-fault group: F.00 is the flow sensor, F.01 the return sensor, F.02 the DHW sensor, F.06 the draught sensor, F.07 the solar collector return sensor, F.08 the water heater grounding fault, and F.09 the flue/hood sensor.

Causes, fixes & costs for Protherm F.08 → · All Protherm codes

Frequently asked questions

Is the F08 fault code the same on every boiler?

No. F08 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 F08 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a F08 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.