draughts heat loss

ive had a new boiler fitted and its fine but notice i have a draught at the top of my stairway ive pvc windows and doors fitted and loft insulated but still have a very bad draught has anyone any idea off i can find where its coming from

There can be loads of options , trickle vents or open windows , even if you loft is insulated it still has to breathe around the perimeter does your loft hatch fit snuggly in its hole ? Check your external doors for weeping seals etc. Obviously it comes from out doors so where ever you have an opening to the outside world ( vents and pipes too ) check them with a damp hand to feel for a breeze.

Is your new boiler in a cupboard at the top of the stairs?Check the vent pipe,or you might have a few floorboards not been put back down,mudge is right follow your condensate pipe to where it exits.

a naked candle will flicker in a breeze,and if you had smoke would see it move away from drafts also.

could be the pipe vent the hole could be too large loft hatch might be off slightly or your window frame has cracked from the brick