High
F.78 on Vaillant ecoTEC Pro 30

Your boiler has lost communication with the device that monitors your hot water temperature, causing it to stop producing hot water.

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

Interrupt.: DHW outlet sensor on ext. contr. | UK link box is connected without the domestic hot water temperature sensor being bridged

From this model's manual
Verified against the Vaillant Ecotec Pro 30 installation & service manual, page 37.
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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Related fault codes

F.77View →F.78View →

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