I don't know if it's due to narrow heels, but I get terrible heel blisters every time I hike up steep terrain. I keep trying different boots, but I haven't found one that works yet. I do a lot of winter climbing and need warm boots that work with crampons, otherwise I'd just use running shoes (which I do in the summer). I try different lacing techniques and use lots of mole skin, but it doesn't fix the problem. With some boots, I am able to keep my heels from slipping, but the force on my heel causes more damage than the slipping.
The only boots I've used without heel pain were plastic mountaineering boots, but I really hate carrying those massive things around. Especially since the climbs I do tend to have long approaches.
I guess I need to look into the custom fitting that was mentioned before.