My response would be to ask how you would deal with a declaration of, "I lift the large boulder with my bare hands." At that point, the player has made a clear declaration of their action, exactly as when they declared they'd turn the dial to 'S'. So, as long as the player just declares and doesn't ask or state that their uncertain, it's good, no check?
Obviously, that's wrong, so the problem here is one of skipped steps. The player declaring he turns the dial to 'S' is a physical action absent a motivation. We're left would knowledge of how the player determined to perform that action. If we knew, then we'd probably understand that the player deciphered the puzzle and arrived at an answer he thought was correct, then made a declaration for his character with the puzzlinging as an unspoken fait accompli. Had he asked if his character could come to this conclusion, though, both you and Iserth have clearly said that a check would be called for, but because the player didn't ask that question, just skipped it and moved straight to the physical act of completing the puzzle, you're unwilling to consider that such an action took place in an area where you, as the DM, have any say. You've moved something that could be a game mechanic check, and would be if expressed, to the inviolable area of 'player agency.'
But, when I express that I might choose to acknowledge that skipped step, if I ask for a check to cover the solving, I have done something you disagree with. In reality, all I've done is acknowledge the intermediate step and brought it to the fore. The player is free to declare their attempting to solve the puzzle, but the character's ability is in question, so a check is called for. Encouraging players to move into positions where they can effect a fait accompli to bypass the chosen limitations of their players is a disservice to the player -- it says that his choices in where and how to allocate his character building choices are of little matter. It also does a disservice to other players, who may be attempting to honor their own prior choices, or who lack the real life mental acuity to pull such feats off. By encouraging players to avoid the consequences of their own choices by hiding steps and specifically wording actions so as to avoid those choices is encouraging a game I don't necessarily want to play. This isn't a matter of me thinking it's unfair, or that players are cheating and need to be stopped, it the fact that I think that, for a good game to exist, choices must have meaning. The argument here really boils down to different camps placing more or less meaning on some choices. Some feel that the choices made in character creation are as important as choices made in play, others feel that character creation choices are nearly inconsequential to choices made in play. I belong in between the two extremes, but have enough of a foot in 'both matter' to say that, occasionally, if I notice a trend in attempting to negate or lessen the impact of choices made earlier through specifically worded play declarations, I may take action to adjust and make those earlier choices more consequential.