In reply to Fenda:
I once had " splitting heel" pain from my winter boots about 10 years ago while on a weeks winter walking trip around Scotland.
From your description of sore red heels, this is maybe not what you have experienced.
I have fairly flat feet ( not much of an arch) and have heel spurs, which if you Google "spitting heel pain" seems to be a common factor.
It is strange though, since I had this pain it has never come back. It was extremely painful, I even stopped in the hut for a day to rest while the others went out.
If your problem is rub related you can try a few different things:
Volume adjusters I.e flat insoles, try heel only ones or a full insole.
Different lacing options, to stop heel slippage.
Wear a thin liner sock under your thick ones.
Tapping
Unfortunately if you find that none of these work you may have to change your boots : (
Post edited at 11:56