Bubba, the recirculator pump, usualy a B&G moves the water through the
system to Heat more evenly then old gravity systems. A common retrofit
50 - 60 yrs ago. If aqua stat is set say at 140 but house thermostat is
still calling for heat the pump will just run till water gets to say 135
then refiring the boiler. Pump stuts off when house thermostst is
satisfied.