Vaillant boiler fault code f25

vaillant boiler fault code f25

Flow temperature rising dramatically fast (5 degrees per second or so)

Why it happens

  1. The appliance or system has gotten blocked or air-locked causing the main heat exchanger flow pipe to heat up too rapidly.
  2. Blocked or faulty pump
  3. Water not moving in the system
  4. Improper calibration of the heating flow NTC thermistor. Make sure it reads 12Kohms and 20 degrees)
  5. Improper calibration of the heating return NTC Thermistor. Make sure it reads 12Kohms and 20 degrees)