Place the temperature sensor of the water heater at room temperature. Connect the two probes of the digital multimeter to the two pins of the thermistor and measure its actual resistance. Then compare the measured actual resistance with the nominal resistance. If the actual resistance differs by ± 2 ohms from the nominal resistance, it is considered normal. On the contrary, the performance of thermistor temperature sensors deteriorates or even damages. Alternatively, the thermistor can be subjected to heating detection using a lighter. If the resistance value of the multimeter decreases with increasing temperature, it indicates that the thermistor temperature sensor is functioning properly. If the resistance value remains unchanged, it suggests that the thermistor temperature sensor is damaged.

Due to the fact that the platinum resistance temperature sensor has three lead wires, it is difficult to find which wire of different colors to connect with one of the multimeter probes. Connect the other probe to two additional leads. If the resistance values measured separately are found to be infinite or lower than 100 ohms after pairwise measurements, it indicates that the platinum thermistor is damaged. If the resistance values are different after two measurements, it indicates that there is a problem with the compensation wire or its lead wire of the platinum thermistor. At the same time, the platinum thermistor can be manually heated. If the resistance value does not change, it indicates that the platinum thermistor is damaged. If the measured actual resistance value differs significantly from the nominal resistance value, it indicates that the performance of the platinum thermistor is deteriorating.

A temperature sensor is a variable resistor controlled by temperature, which can be measured in the 100K resistance range. If it is a sensor with a negative temperature coefficient, the resistance value will decrease when heating the sensor. If it is completely open circuit, there is no need to measure it, it is definitely broken. If the temperature of the temperature sensing part of the sensor changes, but the resistance of the sensor does not change, then there is also a problem!