landlord shut heat off but i have hot water, how do i turn on the heat brrr?

i have hot water but no heat(furnace is oil heat and controls both heat and hot water)...the landlord told me he did this somehow bcuz the furnace also heats another rental unit and he doesnt want to heat the other place bcuz they havent paid rent and i told him that was fine bcuz it wasnt cold at night yet but now it is and he's away on a cruise somewhere and of course not answereing my calls so is there a valve to open or a switch somewhere?? any help is appreciated plz respond to my email k.g (AT) mail (DOT) com