Reduced or stopped flow during cold weather calls for a cautious inspection, not open flame or improvised high heat.
The short answer
Stop relying on the affected fixture and check whether other hot and cold outlets work. Look only from safe, accessible areas for frost, swelling, or water. Keep the main shutoff reachable because a frozen section can leak after thawing. Arrange qualified help when the location, pipe condition, or safe heating method is uncertain.
What to notice
Map the loss of flow
Record which fixtures have no flow, weak flow, or normal flow. Test gently and avoid leaving a faucet unattended. A pattern may help narrow the branch, but concealed routing remains uncertain. Tell the provider about exterior walls, unheated cabinets, crawl areas, or recent heating interruption without opening building materials.
Use a firm heat boundary
Do not use a torch, open flame, unattended heater, or electrical device in a wet area. Massachusetts public guidance emphasizes prevention and maintaining heat. The correct response depends on access, pipe material, surroundings, and manufacturer requirements. A person on site must decide whether any warming method is safe.
Look beyond the immediate thaw
Ask what exposed the pipe to freezing and how recurrence can be reduced. Insulation, air leakage, heat distribution, exterior faucet preparation, and vacancy planning can involve separate work. A restored trickle does not prove that a pipe or connection remained intact. Check for water as flow returns.
One useful question
Should I pour boiling water on a frozen pipe?
No general article can make that safe for a particular pipe or surrounding material. Avoid sudden, uncontrolled heat and any flame. Call a qualified provider when you cannot identify an accessible section and a safe method. Be ready to shut off the supply if leakage appears.