We set the heat lamp up for our last litter (this is only our second litter!) and they didn't go anywhere near it, but there was only three and it was August last year. I did the same again this year and, actually, they've used it loads, only going back to mum for feeding it seems! We were hoping the same for our runt but he snuffed it - I doubt we would have been able to get rid of him when 'the time' came so we would have had a boar to keep too probably!