BoilerFaultCodesWhat the manual says
Manufacturer manualReturn-NTC: - NTC broken - NTC cable broken - Defective connection at NTC - Defective connection at electronics | Return-NTC cable defective/broken NTC faulty
From this model's manual
Verified against the Vaillant Turbomax Plus 824 828e installation & service manual, page 40.
What causes this fault?
This fault occurs when the boiler's return sensor fails to communicate the water temperature back to the main control board. The most common reason is that the sensor's internal electrical resistance has failed due to age, or the thin wiring connecting it to the computer has become loose or damaged.
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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