Thawing a frozen pipe safely
Turn off the water at the stopcock first. Thaw the pipe gently from the tap end using warm, not boiling, water, a hot water bottle or a cloth soaked in warm water. Never use a naked flame, blowtorch or direct high heat, as this can crack the pipe or cause a fire.
When to call a professional
If you cannot reach the frozen section, the pipe has split, water is near electrics, or thawing does not restore flow, stop and arrange professional help rather than risk further damage.