Frozen pipes in top floor of a terraced rented flat?

been reading a few questions about the same problem . i have had a hair dryer on the only part of my main inlet pipe i can access for around 3 hours now. as i live on 1st floor and cant access anything below do you think i am wasting my time here .would the pipe eventually thaw using the hair dryer or would the pipe be frozen too far away for it to have any affect on it. your views please.