An installer needs to connect a thermal storage tank that’s heated by a renewable energy heat source, along with a mod/con auxiliary boiler. Both will supply a common load.
When a heating load is present, and the load circulator turns on, the tank is to supply the load if the water at the aquastat is at or above 140°. In this case circulator (P1) needs to run and circulator (P2) and the auxiliary boiler should be off. If the temperature at the aquastat is less than or equal to 130°, the auxiliary boiler should be on, circulator (P1) should be off, and circulator (P2) should be on.