AquaCal Defrost Sensor Kit 6105D Temperature Sensor (STK0021) features a 10K ohm thermistor sensor (ECS6105/6105D) with insulation, designed to monitor water and defrost temperatures in AquaCal pool heat pumps. This kit ensures accurate temperature regulation, preventing freeze-ups, with a straight sensor for easy installation in various heat pump models.Compatible with AquaCal TropiCal, SuperQuiet, and other heat pumps (e.g., SQ125, 115AHDSBTB), per AquaCal specs.Specs: 10K ohm sensor; includes 6105D sensor, insulation; fits STK1113A black plastic or 1113KIT copper wells; UL-listed.Installation: Inserts into water inlet line or sensor well with hose clamp; tools: 11/32" or 3/8" drill bit, screwdriver; snug clamp to avoid damage.Features: Fixes OTA error codes; durable construction for harsh pool environments; insulation ensures reliable readings.