It does tend to get warm and toasty above these heaters and to a degree this is normal, if you suspect it's too much, then I'd put your had down the back and check both ducting pipes are attached to the fan housing.
They should have a screw to stop them falling out but this can be missing allowing the duct to fall free and the hot air to escape into the space behind the fire. Of course if this is so, the outlets in that duct won't be delivering much if any hot air and this should give you a clue.