This　paper　describes　the　experiment　carried　out　to　analyze　the　effects　of　improper　refrigerant　charge　and　incorrect　TXV　(Thermal　Expansion　Valve)　opening　on　the　air-source　heat　pump　water　heater　using　R134A.　The　performance　of　the　system　were　measured　in　combinations　of　four　refrigerant　charges　of　70%,　85%,　100%　and　115%　of　the　optimal　value　and　three　TXV　opening　of　30%,　45%　and　60%　of　full　opening　at　ambient　temperature　of　20D/15W　(dry-bulb　temperature/wet-bulb　temperature).　The　results　showed　that　the　maximum　COP　was　nearly　33%,　31.9%　and　4.4%　higher　than　that　of　70%,　85%　and　115%　of　the　optimal　refrigerant　charge　at　60%　TXV　opening,　respectively.　And　it　was　found　that　the　increase　in　TXV　opening　can　enhance　COP　when　water　temperature　exceeded　30°C.　©　2015　Taylor　&　Francis　Group,　London.