Pipes run through unheated porches, exterior walls, and basement corners in most Boston triple-deckers. When outdoor temps stay below 20°F with wind chill, kitchen lines on north-facing walls freeze first — often before owners notice reduced flow.
Prevention: open cabinet doors under sinks on exterior walls, keep thermostat at 55°F minimum when away, and insulate hose bibs in October. Know your main shut-off — usually near the water meter in the basement. If a pipe is frozen but not burst, gentle warm-air (hair dryer, space heater) may thaw it; never use open flame.
If water stops or you see a split fitting, shut off the main immediately and call a licensed plumber. A small crack can release hundreds of gallons into finished ceilings. Renters: notify your landlord the same hour — mold follows within days in humid basements.
Not sure if it's a partial freeze or failing valve? Upload a photo on Opa Pro — get a quick triage and a fair local plumber price range.