All error codes are on "Cfnetwork Errors codes References" on the documentation
A small extraction for Cfurl and cfurlconnection Errors:
Kcfurlerrorunknown = -998, kcfurlerrorcancelled = -999, Kcfurlerrorbadurl = -1000, kcfurlerrortimedout =-10
Kcfurlerrorunsupportedurl = -1002, Kcfurlerrorcannotfindhost = -1003, Kcfurlerrorcannotconnecttohost =-1004, Kcfurlerrornetworkconnectionlost = -1005, kcfurlerrordnslookupfailed = -1006, Kcfurlerrorhttptoomanyredirec ts = -1007, kcfurlerrorresourceunavailable = -1008, kcfurlerrornotconnectedtointernet = -1009, Kcfurlerrorredir Ecttononexistentlocation = -1010, Kcfurlerrorbadserverresponse = -1011, Kcfurlerrorusercancelledauthentica tion = -1012, kcfurlerroruserauthenticationrequired = -1013, Kcfurlerrorzerobyteresource = -1014, Kcfurl Errorcannotdecoderawdata = -1015, Kcfurlerrorcannotdecodecontentdata = -1016, Kcfurlerrorcannotparseresponse = -1017, Kcfurlerrorinternationalroamingoff = -1018, kcfurlerrorcallisactive = -1019, Kcfurlerrordatano tallowed =-1020, kcfurlerrorrequestbodystreamexhausted = -1021, kcfurlerrorfiledoesnotexist = -1100, Kcfurlerrorfilei Sdirectory = -1101, Kcfurlerrornopermissionstoreadfile = -1102, Kcfurlerrordatalengthexceedsmaximum = -1103,