I've done the same (bought a house, kept the old one for rental) and used an agency as a middle man. They take care of collecting rent, and the day to day business if, say, a plumber needs to be called (I just have to sign off on it). This at a 6% fee of the monthly rent is quite worth it to avoid any hassle. The rent income also fully covers the mortgage of the new house so basically my living costs are for free.