If your hot water line is frozen, you need to thaw it slowly, safely, and be ready to shut things down fast if you spot a leak. Here’s a practical, homeowner‑level guide.

First: Safety and Quick Checks

Before you start, do a quick assessment:

  • Check if it’s only the hot water not working at a fixture (sink/shower) but cold water is fine. That strongly suggests a frozen hot water line, not a total supply issue.
  • Look and listen for:
    • Bulging pipes
    • Hissing/spraying water
    • New damp spots on ceilings, walls, or under sinks
  • If you see or suspect a burst (even a pinhole leak):
    • Turn off the main water supply to the house immediately.
    • If water is near electrical outlets or your panel, switch off power to that area and avoid standing water.

If you cannot find the main shutoff or feel overwhelmed, this is the moment to call an emergency plumber, not to experiment.

Step‑By‑Step: What To Do Right Away

These steps apply when you suspect a frozen hot water line but do not yet see active leaking.

  1. Open the hot faucets
    • Turn on the hot side of the affected taps (especially the one closest to where you think the line is frozen).
    • Slight drips help relieve pressure and give thawed water somewhere to go.
    • If multiple hot taps are on the same line, crack several open a little.
  2. Turn down demand on the water heater
    • Set the thermostat on the water heater to a lower temperature or “warm” rather than “hot.”
    • Do not crank it hotter to “force” thawing; that just stresses pipes and the heater.
  3. Locate likely frozen sections
    • Common spots:
      • Exposed pipes in unheated basements, crawlspaces, garages
      • Pipes in exterior walls behind kitchen/bathroom cabinets
      • Lines running near drafty windows or doors
    • Feel along accessible hot water pipes with your hand:
      • Very cold sections, frosty areas, or condensation can mark the frozen spot.

Thawing the Hot Water Line Safely

Use only gentle, controlled heat, and stay with it the entire time.

Tools you can safely use

  • Hair dryer (most common)
  • Small space heater pointed near (not right on) the pipe
  • Warm towels (soaked in hot water, then wrung out)
  • Commercial electric heat tape (if you know how to use it and can follow the instructions closely)

How to thaw

  1. Start near the faucet and work backward
    • Begin warming the pipe closest to the fixture, then move slowly toward the colder sections.
    • This lets melting water escape instead of getting trapped behind more ice.
  2. Move heat continuously
    • With a hair dryer: keep it moving back and forth along a 12–18 inch section of pipe.
    • With warm towels: wrap, leave for a few minutes, then re‑warm and re‑wrap as they cool.
  3. Keep faucets slightly open
    • As ice begins to melt, you may hear gurgling and see a trickle of water.
    • Let it run; running water helps speed the thaw.
  4. Watch for leaks constantly
    • During thawing, a pipe that cracked earlier may only show itself once water starts flowing again.
    • The moment you see a leak:
      • Shut off the main water.
      • Stop applying heat in that area.
      • Call a plumber or your building maintenance.

What Not To Do (Very Important)

Avoid these common “hack” methods; they can cause fires, pipe damage, or serious injury:

  • Do not use:
    • Open flame (propane/“plumber’s” torch, lighter, candles)
    • Charcoal or gas heaters indoors
    • Ovens or stoves as room heaters
    • High‑heat industrial heat guns close to combustibles
  • Do not:
    • Pour boiling water directly on fragile plastic pipes or fittings
    • Hit or bend the pipe to “break the ice loose”
    • Ignore signs of a hidden leak (mysterious dripping sounds, wet drywall, or ceilings)

If the Frozen Section Is Hidden in a Wall

Sometimes the hot water line that froze is inside an exterior wall or behind cabinets. You can try:

  • Raising room temperature
    • Turn up the thermostat several degrees.
    • Leave cabinet doors open under sinks on exterior walls to let warm air in.
  • Targeted warm air
    • Aim a space heater at the wall or open cabinet front from a safe distance.
    • Keep it far from flammables and never leave it unattended.

If you don’t get any improvement within an hour or two, or the wall feels swollen or damp, stop and call a professional. Cutting into drywall to access the pipe is often a job for a plumber or contractor, especially if there’s potential water damage.

Protecting Your Water Heater

When only the hot line is frozen, your water heater is part of the system, so treat it gently:

  • Don’t let it fire constantly against a fully frozen line; turn the temperature down if no hot faucets are flowing at all.
  • In severe cases (no hot flow anywhere and you’re leaving the house), you may:
    • Turn off power to an electric water heater or set a gas heater to its lowest setting or “pilot.”
    • Consult the heater’s manual before shutting everything down if you’re unsure.

If the water heater itself or the short hot outlet pipe above it appears frozen, shut off power/gas and water supply to the heater and call a pro immediately. That combination can become dangerous quickly if a tank connection fails.

When You Should Call a Plumber

It’s time to get professional help if:

  • You can’t find your main shutoff valve.
  • You suspect a burst pipe (even if you don’t see it yet).
  • You see bulging pipes, cracking sounds, or wet spots in ceilings or walls.
  • The frozen section is inaccessible (inside walls, ceilings, or under a slab).
  • You’ve tried gentle thawing for an hour or two with no improvement.
  • You’re in a multi‑unit or rental building where you might affect neighbors’ lines.

In rentals or condos, also notify your landlord or management right away; frozen hot lines can damage shared plumbing.

Preventing the Hot Water Line from Freezing Again

Once you get things flowing, immediately plan prevention:

  • Insulate vulnerable pipes
    • Use foam pipe sleeves or wraps on exposed hot and cold lines in basements, crawlspaces, garages, and near exterior walls.
  • Eliminate drafts
    • Seal gaps where pipes pass through walls, floors, or sill plates.
    • Check around hose bibs, vent openings, and foundation cracks.
  • Keep indoor areas warmer
    • Avoid setting the thermostat too low in extreme cold (typically keep at least around 55–60°F / 13–16°C).
    • Leave interior doors open so warm air circulates.
  • Use “drip protection” in deep cold
    • In extreme overnight temperatures, leave a small, steady drip from the farthest hot and cold faucets.
    • This is especially helpful on known problem runs, like kitchen sinks on exterior walls.
  • Consider heat tape for chronic problem lines
    • Electric heat cables, properly installed and used as directed, can keep exposed runs from freezing.
    • If you’re unsure which product is safe for your pipe type, ask a plumber to install it.
  • Long‑term fix: reroute the line
    • If the hot line in a particular wall freezes every winter, the real cure may be rerouting that section through a warmer interior path.
    • This is more invasive and costly but saves repeated emergencies and potential water damage.

“Quick Scoop” Recap (In Plain Language)

  • Confirm it’s only the hot line; check for leaks or bulges first.
  • Open affected hot faucets to relieve pressure.
  • Use gentle heat (hair dryer, warm towels, room heat) starting near the faucet and working back.
  • Never use open flames or risky DIY methods.
  • If you see leaks or the pipe is hidden and not improving, shut off water and call a plumber.
  • Afterward, insulate, seal drafts, and consider heat tape or rerouting to stop this from happening again.

If you tell me what part of the house the hot water stopped in (kitchen, bathroom, specific floor) and what temperatures you’re dealing with, I can walk you through a more tailored, step‑by‑step plan for your situation.