Hi all, first post!

Installed a oitsein water heater couple of years ago and it’s slowly leaking from the outer casing and there’s a little hole by the thermostat that seems to be dripping every few minutes regardless of the hot water being used? 
Il see if I can post a pic but is this normal? Has the guy who fitted done something wrong or do they simply not last here? The old one was centuries old no issues except it didn’t provide enough hot water