Same problem with mr steam iron?

I have had this iron for under a year and i have the same problem as everyone else where the standby light will not go out and just bleeps every time i press the steam button. This was a replacement to my original iron and my 2 yr guarantee is out by 4 months now they are offering me a reduced price iron.
I know this can be fixed, please can someone tell me how i try the white vinegar, does it go into the water compartment diluted with water or on its own?