Abstract: A plumbing assembly maintains temperature equilibrium of a hydronic heating system irrespective of the type of heat source used. The assembly facilitates all control methods characteristic of such heating systems through use of a heat loop, a pair of heat traps, a balancing valve and a controller. The plumbing assembly includes a zone supply conduit and a zone return conduit. The heat loop includes a first conduit with a supply end and a return end. A bypass valve is coupled between the supply end and the return end for controlling the flow of fluid through the heat loop. Two heat traps are provided, which comprise a first looped conduit connected to the first conduit upstream from the bypass valve, and a second looped conduit connected to the first conduit downstream from the bypass valve. An injection pump connected downstream from the first looped conduit draws fluid from the heat source injecting it into the system via the supply conduit.