Your boiler's internal sensor that monitors exhaust gases has developed a fault, causing the system to shut down for safety.

Hot Water NTC Fault

What causes this fault?

This fault occurs when the boiler's internal safety sensor detects that the exhaust gases are too hot or if the sensor itself has suffered an electrical failure. Over time, the sensor can degrade due to constant exposure to heat, or the wiring connecting it to the main control board may have become loose or damaged. Because this component monitors high temperatures, the boiler shuts down immediately to prevent any internal damage.