There is an implied Warranty of Habitability when you rent a premises in Pennsylvania. In other words, the rental unit must be habitable: i.e. there must be water and heat, and the property must be safe and sanitary.
If a problem develops after you move in, contact the landlord immediately. While I recommend calling the landlord, send a follow-up confirmation letter/email. Make sure that all communication is documented. Also, keep a copy of any written correspondence for your records. (Do not record phone conversations).
If the issue is not resolved within a reasonable time-frame, then let the landlord know that you are placing the rent into an escrow account until such time as the problem is resolved. You may also let the landlord know that you will be fixing the problem yourself with the costs deducted from the following rent payment.
If the landlord disagrees and you find yourself in court, bring pictures and copies of your correspondence, as well as proof that the rent is in an escrow account. When you see the judge, you may receive an abatement of rent for the time that the premises was not habitable.
TransUnion article: What does the Implied Warranty of Habitability Mean?