When failing a forge attempt, set the amount of heat held to zero instead of destroying the fire crystals.
Lets go with the following odds of succeeding-
1x = 15% success chance = heat every weapon 6-7 times = 151 rads total
2x = 40% success rate = heat every weapon 2-3 times = 302 rads total
3x = 100% success rate = heat every weapon once = 453 rads total
Just think of how the players would react to this! They hold onto their fire crystals and use 1x until they get more fire crystals and then they move on up, making their fire crystal usage scale accordingly, no more being locked out of T3, because hey, enough t2 runs will net you a cheap level up.. but all of that still takes time and effort, just in a different, friendlier way.
You can still buy heat amplifiers and radiants from the shop, and those things still speed you up drastically because you're going from 1x to 3x or maybe you're just doing a lot more 1x on a lot more items, who knows. Forge prize box etc. could still exist as well with this, as they sweeten the deal.
If you're going to do anything about the forge or radiant fire crystals I think this might be the way to do it.
Well, it would give a use to heat amplifiers aside from forcing one to get fire crystals faster