In a heat pump pool heater, undesirable compressor-created pressure spikes resulting from start-up of the heater after extended idle periods thereof are substantially eliminated by the incorporation in the heat pump refrigerant circuit of a specially designed pressure spike eliminator structure. The spike eliminator structure includes an enclosed hollow wall structure extending around a first refrigerant tubing portion disposed between the heat pump circuit compressor and condenser and forming a cavity around the first refrigerant tubing portion, and a transfer tube directly connected to a second refrigerant tubing portion disposed between the condenser and expansion valve and intercommunicating the interiors of the cavity and the second refrigerant tubing portion.