The map on p. 308-309 of the 8th edition of Rick Steves's Portugal (2015) gives an incorrect location of the laundromat.
Lavandaria do Infante
Rua do Comercio do Porto 43/45
Open daily 0830 - 2200
3 small washers, 5 euros, 60 minutes
2 dryers 2 euros 15 minutes
facebook.com/lavandariadoinfante
Free internet, password case sensitive