As part of Nick Valentine's quest line you need to have dogmeat help you searching. When this happened (it happened automatically to me) I had Preston in power armour with me.
He was sent away (and the dialog to send him away appeared) and he was wearing power armour. However once I returned to Sancuary he was no longer wearing the power armour, and there is no power armour icon on my map to indicate where he left it (if anywhere!).
Also, prior to giving him this set of armour, I'd left a previous set outside another random house (because I glitched through the window by sitting on a seat (teleporting myself inside) and that icon is also gone, as I can't recall exactly where it is, I can't go back and get this armour either.
Is there anyway to find these 'lost' armours?
Best Answer
When companions are dismissed, they get out of their power armor before departing. So Preston's armor is wherever you picked up Nick (probably the Overseers office in Valut 81 if it was your first meeting, or perhaps in the detective agency).
As to the armor you left outside somewhere random, you'll just have to retrace your steps, unfortunately.