The issue here is that Hermetic/medieval/elemental principles of association are being used, and while association is a component of spellcasting which one should not disregard entirely, there are complexities to it which are being seriously handwaved when someone says "fire is associated with purification."
Certainly, to one who has trained to associate the two, the thematic linkup can be a powerful associative force, especially in Thaumaturgy.
However, the mistake in the DFRPG is to take that association and use it to justify bypassing genre mechanisms and precedents set up which establish as part of the Dresden Files fiction that doing X is just not easy to do with magic, where X can be healing, mind control, and any number of other things which we are used to doing in systems like D&D.
The effect people want can be termed "black box magic." We don't know why it works, but it does, if you are level Y, studied for an hour or two the night before, have components A, B and C, wave your hands and stand in one place for a set amount of time, *this* happens.
What has been set up in the fiction, however, is that the "black box" element has been discarded, and magical effects require more stringent justification, in terms of mass and energy, conservation of matter, etc. Some of this is elided in-game (were-ravens are a serious compromise of the conservation of matter), and certainly magic isn't fun to play with if everything becomes a logistical problem. We're encouraged to pain in broad strokes,
But the fundamental issue is that Evocation - on its own - is just way too crude to do a lot of these things, no matter what the Hermetic elemental system says. And even Thaumaturgy - stripped of a guiding influence - is somewhat limited by human understanding.
Where a lot of these things get sewn back together is Sponsored Magic: letting a barely comprehensible intelligence do the heavy lifting, when it serves their agenda, and fits in their baileywick.
So, heat associated with healing? Summer Faerie magic. Heat used to soothe tired muscles? Probably thaumaturgy, MAY-be Evocation, with a lot of skill and some medical/biological knowledge.