Something happens when you don’t tune your piano for a long time. Every year that passes by, the pitch drops further and further away from where it should be, and it becomes harder for me to pull it back up to its proper tension levels. Pianos generally go flat during our long winter months, and do not necessarily rise back up to where they were in the summer. Also if a piano hasn’t been tuned for 5-10 years it would probably drop between a semitone or tone, requiring this pitch raise.
I would have to raise the tension of over 200 strings, which puts a lot of strain on the piano’s structure. It’s impossible to make such a big jump in pitch and have a stable tuning in one pass. So what I do is first raise all the strings to their proper average tension levels, then perform a fine tuning, extending the time taken up to 20 minutes extra.
Please note if the strings are rusty or very old, the tension can be too much and cause a string to break. If this happens in a pitch raise, the string would be immediately repaired and the pitch raise would be abandoned, so the piano will be tuned to itself, not at concert pitch. In essence the piano will sound perfectly in tune but will be transposed down a semitone or tone.