2nd floor bathroom sink backup w/no water source
We're having a plumbing problem that has us stumped.
We're in the early stages of remodeling a bath on the second floor. The water supply to the sink we're having a problem with is capped off and the sink has not been used for about three months.
Yesterday water started backing up in the sink and overflowed onto the floor. The water was clear and had no odor. We're having no plumbing problems in the rest of the house and so far the sink hasn't backed up again.
Any ideas on what caused the sink to backup?
Thanks for your help,