High
F.84 on Vaillant ecoTEC Pro 30

Your boiler has detected that the water temperature readings at the start and end of its heating circuit do not match up properly, causing it to shut down to prevent damage.

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

Fault: NTC temp. diff. implausible | Temperature difference is implausible

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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