Caleffi’s line of hydronic heating zone controls — the ZSR101, ZSR and ZVR series — feature heavy-duty sealed relays for quiet operation; large screw terminals for ease of wiring and on-board ground terminals; and are compatible with two-, three- and four-wire thermostats or other low-voltage controllers with switching action. The ZSR pump controller and ZVR valve controller models are expandable to an unlimited number of zones using simple three-wire connection between controls.
Caleffi hydronic heating zone controls
![Caleffi hydronic heating zone controls](http://www.pmmag.com/ext/resources/PM/2016/Feb-2016/PM0216_Products_Caleffi.jpg?1455741163)