As　a　substitute　for　R22,　an　environmentally　friendly　zeotropic　mixture　R417A　is　often　employed.　The　large　glide　temperature　of　the　zeotropic　mixture　R417A　could　cause　capacity　and　efficiency　reductions　due　to　changes　in　its　composition　after　an　isothermal　vapor　leak/recharge　process.　It　is,　therefore,　necessary　to　predict　the　composition　change　in　R417A　under　all　leak　conditions.　This　paper　presents　the　experimental　analysis　of　the　mass　composition　of　R417A　in　the　presence　of　a　0-50%　isothermal　vapor　leak/recharge　in　a　heat　pump　water　heater　Based　on　the　experimental　data,　a　simple　model　is　proposed　to　describe　the　composition　change　in　R417A　for　various　leaks　and　recharge　scenarios.　The　effect　of　composition　change　in　the　performance　of　a　heat　pump　water　heater　is　also　dealt　with.　Experimental　results　show　that　the　composition　changes　in　R417A　increase　as　ambient　temperature　decreases.　Isothermal　vapor　leaks　have　a　great　effect　on　the　composition　of　R417A　and　the　performance　of　a　heat　pump　water　heater　at　lower　temperatures.　It　is　also　found　that　when　the　ambient　temperature　is　higher　than　7　degrees　C　with　a　10%　leak　and　R417A　recharge,　there　is　almost　no　difference　in　the　performance　of　the　plant　with　respect　to　the　original　state　except　that　the　compressor　discharge　temperature　is　lower　[DOI:　10.1115/1.4000173]