Where are boiler overflow pipes usually installed?

dgh19

I live in a block of flats and for the past couple of weeks water has been running down the side of the building out of one of the overflow pipes above me in the middle of the night and getting though my window.
What I am having trouble figuring out is which apartment the water is coming from. Are boiler overflow pipes usually installed above or below each flat? There doesn't seem to be a pipe above the top floor flat nor can I find a pipe below the ground floor flat. 
Property management haven't been very quick to reply yet, but I'm just curious to find out who's going to be paying the water bill. 
Thanks in advance.

nofoollikeold

1. May not be a boiler, could just as easily be a WC cistern or a cold water tank's overflow.
2. Boiler pressure relief pipes normally come out just below the level of the boiler, but given that the boiler could be mounted at the top or bottom of a wall, the pipe could be almost anywhere below the ceiling of the flat.  
3. The same goes for WC and cold tank overflows.
4. Given that the water comes out at night, my first guess would be a WC.  Water pressure goes up at night because no one is using much water.  If the float operated valve is a bit weak, the extra pressure can cause it to let water past, which then reaches the overflow.

Murmansk

Boiler pressure relief pipes usually come out and then do a U turn back towards the wall - so that scalding hot water runs down the wall rather than landing on someone like it would from a hosepipe.