Domestic hot water zone valve controlled external coil

Claim 1

A domestic hot water zone valve controlled external coil comprising in combination: (a) an external tankless domestic hot water coil which acts as a heat exchanger whose heat source is the output of a hydronic boiler wherein heated water is cycled from the outlet of said hydronic boiler through said external tankless domestic hot water coil and back to the inlet of said hydronic boiler whereby cold water enters said external tankless domestic hot water coil and is heated thus providing domestic hot water; (b) an aquastat whose electrical contacts close when the temperature of said domestic hot water falls below some predetermined value; and, (c) an electric zone valve with end switch placed in the fluid circuit between the return line of said external tankless domestic hot water coil and the inlet line of a circulator boost pump used on an existing heating zone, whereby, when said circulator boost pump is operating and said contacts of said aquastat close, an analysis and switching circuit causes said electric zone valve and end switch to actuate thereby allowing said heated water to flow through said external tankless domestic hot water coil, said analysis and switching circuit which determines whether said electric zone valve or said domestic hot water circulator pump operates comprises two AND gates whose inputs are an aquastat contact closure signal and a circulator boost pump operating signal whereby one of said AND gates has an output signal which activates a relay which in turn activates said electric zone valve with end switch when both AND gate inputs are positive which corresponds to a condition in which said existing circulator boost pump is operating and said aquastat calls for increased hot water and whereby the other of said AND gates which has an inverter in said circulator boost pump operating signal input has an output signal which activates a relay which in turn activates said existing hot water circulator pump when said aquastat contact closure signal is positive and when said circulator boost pump operating signal is negative which corresponds to a condition in which said existing circulator boost pump is not operating and said aquastat calls for increased hot water.