The Vaillant wall-mounted heat exchanger module divides the heating system circuit from the circuit for the heat pump. Due to the fact that the heat pump is installed outside the building and is therefore exposed to changing weather conditions it is essential that the fluid passing through the heat pump be frost-protected to prevent the heat pump from being damaged by freezing. The heat exchanger module enables connected glycol circuits to be segregated from heating circuits because it can be expensive to fill the entire heating system with glycol. When radiators are removed or drained and refilled the heat is lost.