Tekmar 664 Snow Detector & Melting Control Two Zone, Two Stage Boiler & Mixing Snow Detector & Melting Control 664 The Snow Detector & Melting Control 664 is designed to operate mechanical equipment to melt snow off of up to 2 outdoor slabs. It can be used in hydronic snow melting applications consisting of up to 2 zones and 2 boilers where each zone can operate at an independent temperature. This product uses a tekmar snow/ice detection sensor in order to automatically melt snow in a priority sequence while protecting the boiler plant with a mixing device. It is capable of controlling up to 2 boilers, a variable speed or modulating (4-20 mA) mixing device, a mix system pump, and 2 zone pumps.