A double-wall heat exchanger comprising: a plurality of heat transfer plate pairs (12; 14), each heat transfer plate pair (12; 14) forming a double-wall structure comprising two heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) that are at least partially separated by a leak space , wherein each of the heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) having a series of undulations to facilitate heat transfer, the leak space positioned between the undulations of the heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) of each heat transfer plate pair (12; 14); at least one fluid port (A, B, C, D) defined through each plate pair (12; 14) within which a heat exchange fluid is distributed either into or out a fluid channel (28; 30; 32; 34) that is defined between adjacent plate pairs (12; 14), wherein two adjacent plate pairs (12; 14) are mated together along a boundary edge of the at least one fluid port (A, B, C, D), wherein the fluid channels are fluidly isolated from the leak spaces , and wherein adjacent fluid channels (28, 32; 28, 34; 32, 28; 32, 30) are fluidly isolated from each other and alternating fluid channels (28, 30; 32, 34) are in fluid communication with each other; characterized by a port vent groove defined between the two adjacent plate pairs (12; 14) at a location surrounding the boundary edge of the at least one fluid port (A, B, C, D), wherein the port vent groove intersects and is in fluid communication with a leak space of one of the two adjacent plate pairs (12; 14); and at least one weep hole that is disposed through the plurality of heat transfer plate pairs (12; 14) and intersects the leak spaces of the plurality of plate pairs (12; 14) to channel leaking fluid within one of the leak spaces or the port vent groove to a location outside of the heat exchanger . a plurality of heat transfer plate pairs (12; 14), each heat transfer plate pair (12; 14) forming a double-wall structure comprising two heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) that are at least partially separated by a leak space , wherein each of the heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) having a series of undulations to facilitate heat transfer, the leak space positioned between the undulations of the heat transfer plates (12 , 12 , 12 , 14 , 14 ; 36, 38) of each heat transfer plate pair (12; 14); at least one fluid port (A, B, C, D) defined through each plate pair (12; 14) within which a heat exchange fluid is distributed either into or out a fluid channel (28; 30; 32; 34) that is defined between adjacent plate pairs (12; 14), wherein two adjacent plate pairs (12; 14) are mated together along a boundary edge of the at least one fluid port (A, B, C, D), wherein the fluid channels are fluidly isolated from the leak spaces , and wherein adjacent fluid channels (28, 32; 28, 34; 32, 28; 32, 30) are fluidly isolated from each other and alternating fluid channels (28, 30; 32, 34) are in fluid communication with each other; characterized by a port vent groove defined between the two adjacent plate pairs (12; 14) at a location surrounding the boundary edge of the at least one fluid port (A, B, C, D), wherein the port vent groove intersects and is in fluid communication with a leak space of one of the two adjacent plate pairs (12; 14); and at least one weep hole that is disposed through the plurality of heat transfer plate pairs (12; 14) and intersects the leak spaces of the plurality of plate pairs (12; 14) to channel leaking fluid within one of the leak spaces or the port vent groove to a location outside of the heat exchanger . <EOS>