High
F.80 on Vaillant ecoTEC Plus 826

Your boiler is struggling to accurately detect water temperatures because a sensor responsible for monitoring the heat exchange process has developed a connection fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Interruption or short circuit of secondary heat exchanger inlet sensor; only in connection with F.91

From this model's manual
Verified against the Vaillant Ecotec Plus 826 installation & service manual, page 50.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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