In reply to Flinticus:
That made me think the problem lay with the toe space. In the shop I was told a tumb width was 'standard'.
Which is more or less correct. The problem is that there is no 'standard'. Every foot is different and every person's preference is different. One person wants a full thumb width, for the other a pinky width is enough.
What kind of boot are we talking about? If it's a general hiking/trekking boot then I would be quite annoyed with a hotspot after a couple of hours. If it's a mountaineering boot and all you develop after a hotspot at the heel after a couple of hours of hiking in them then I wouldn't be all that surprised, especially if they are brand new.