Your boiler is struggling to accurately measure the temperature of your hot water, which usually means it cannot provide a consistent warm flow to your taps.

Hot water NTC sensor defective.

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring your tap water temperature fails or sends an incorrect signal to the boiler's control board. The most common reason is that the sensor has experienced electrical fatigue over time or has developed a loose connection, preventing the boiler from knowing how much to heat the water. In some cases, a build-up of limescale on the sensor can also insulate it, leading to inaccurate readings and this error code.