The overflow pipe which, I presume, comes out of a tank in the attic is letting water out intermitently. The pipe comes out from above my bedroom window, below the roof.

What could be the cause of the problem ?

Thanks in anticipation.

There should be a float ball valve like the one in your toilet that shuts off the flow. This valve needs to be adjusted to where the water shuts off before it gets to the top of the tank Hope this helps, Tom

Try bending the rod holding the float ball down. The farther down it's bent the lower the level. Good luck, Tom