What does the Vaillant F.25 fault code mean?

Your boiler has shut down because the exhaust fumes have become too hot, which is a safety measure to prevent damage to the internal components.

How much does it cost to fix Vaillant error code F.25?

Typical repair cost for the Vaillant F.25 fault is £120-350 including labour.

Vaillant F.25 Fault Code: What It Means & How to Fix It

Technical description

Safety switch off flue gas temperature too high

What causes this fault?

This fault occurs when the internal temperature of the exhaust gases exceeds a safe limit, triggering a shutdown to protect the boiler's plastic components from melting. The most common reason is a buildup of limescale or sludge inside the main heat exchanger, which prevents heat from being transferred to the water and causes it to escape through the flue instead.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.20View →F.76View →

Your boiler has shut down because the exhaust fumes have become too hot, which is a safety measure to prevent damage to the internal components.

Technical description

What causes this fault?

Engineer required

Related fault codes

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