PLEASE be very careful if you're placing the TV above a fireplace in a property that is Victorian or older.
As a builder explained to me, chances are that a 100 or so years of log/coal burning will have perished the mortar between the bricks around the fireplace: as the mortar heats up, it expands, then the fire goes out and because it's very cold during the wee small hours the bricks/mortar cool down relatively rapidly, eventually the mortar cracks/crumbles; for the same reason, the bricks may not be actually attached to the plaster on your room's interior wall (in the vicinity of the fireplace).
Fast-forward to the 21st-century and you wade-in with your rufty-tufty drill to wall-mount a TV, and find that as you drill you're merely pushing the loose bricks out of their slots. Unfortunately, I speak from experience...
Thankfully, I realised what was happening after only a couple of bricks crashed into the grate, which was preferable to somehow managing to attach the fixings and the TV to the wall, only for the TV's weight to pull down the wall and chimney stack a few days/weeks later.
'Er Indoors was not amused...