My Lochinvar Knight has a setting "boiler pump minimum voltage". In the manual it states that as firing rate decreases, the speed of the pump can decrease as well. The range is 2.5-10 volts and is currently at 3.5 volts. First, is there an advantage to using this setting as they state it is for lowering the delta t, and my understanding is that I want a higher delta t? Second, I have a Grundfos UPS 1558-FC, so what is the lowest that the pump will safely handle? Will too low of a voltage hurt it? thanks in advance.