NTC and PT1000 are two common types of temperature sensors, but they operate with a different resistance-temperature relationship.
NTC
In NTC sensors, electrical resistance decreases as temperature increases.
PT1000
In PT1000 sensors, resistance increases with temperature.
Why they are not interchangeable
The controller is designed for a specific sensor curve. The wrong type results in an incorrect temperature reading.
Testing
Resistance is measured and compared against the manufacturer's table.