Description

The Pentair 470180 is the genuine thermistor probe listed as a heater part for the Pentair MiniMax Plus range, sizes 150 through 400.

What it does

A thermistor changes resistance as it warms and cools. The heater control reads that resistance and treats it as water temperature, using it to decide when to fire the burner and when to stop. Everything the heater does about temperature depends on this one signal being accurate.

When to suspect it

If the pool runs noticeably hotter or cooler than the set point, if the display disagrees with a thermometer in the water, or if the heater cycles on and off with no clear reason, the temperature sensor is a reasonable place to look. Confirm the part number against your heater before ordering, since heater probes look much alike from model to model.