A compressor is connected with an evaporator, a condenser, and an electrically controlled valve for circulating a working fluid in a system for recovering waste heat to provide heated water. A controller can be configured to adjust an operating capacity of the compressor to maintain output of a condenser temperature sensor at a condenser temperature set point, except when output of a compressor discharge pressure sensor indicates that a maximum operating pressure of the compressor has been exceeded. In such case the controller reduces the operating capacity of the compressor. The controller may further be configured to shut down the compressor when the discharge pressure sensor indicates that a shutdown pressure has been exceeded.