zero conditional and first conditional

The zero, or present, conditional, using the present tense in both clauses, means, in the words of ‘An A-Z of English Grammar’ by Leech and others, that ‘the condition can be true at any time’. In the case of the example, whenever I press a button, assuming I do, it crashes. In practice, it suggests that the speaker has indeed pressed a button on at least one occasion.

In the first conditional, the main clause envisages the likely result if the condition is fulfilled. In the example, I may or may not press a button, but pressing the button will certainly result in a crash. There is no indication in the sentence that the speaker has yet pressed a button.