How to Thaw a Frozen Pipe Without Causing a Flood
You turn on the tap and get nothing but a trickle, or nothing at all. If it's freezing outside and this is happening on a pipe you know runs along an exterior wall or through an unheated space, there's a good chance it's frozen. Thawing it yourself is often possible, but doing it wrong can turn a frozen pipe into a burst one. Here's how to do it safely.
What you'll need
- A hair dryer, heat lamp, or portable space heater
- Warm (not boiling) towels, as an alternative heat source
- A flashlight, if you're checking a crawlspace or under a cabinet
- Towels and a bucket, just in case
Step 1: Open the faucet first
Before you apply any heat, open the faucet that the frozen pipe feeds, both hot and cold if you're not sure which side is frozen. This does two things. It relieves pressure that builds up as ice inside the pipe starts to melt, and it gives you a way to know the moment water starts flowing again, since it'll usually start as a trickle before returning to normal flow.
Step 2: Find the frozen section
Trace the pipe from the faucet back toward the source, checking for a visibly frozen section (frost on the outside of the pipe is a good clue), an unusually cold section to the touch, or simply the most exposed part of the run, like where it passes through an exterior wall, crawlspace, or garage.
Step 3: Apply heat, starting closest to the faucet
This is the step people get backwards most often. Always start applying heat at the end closest to the faucet and work your way toward the blockage, not the other way around. If you heat the middle of a frozen section first, melting water has nowhere to go because ice is still blocking it further down the line, and pressure can build up enough to crack the pipe.
Safe heat sources include:
- A hair dryer on a low or medium setting, moved continuously back and forth
- Towels soaked in warm water and wrapped around the pipe, reheated as they cool
- A portable space heater aimed at the area, kept at a safe distance from anything flammable
Step 4: Never use an open flame
This deserves its own step because it's the most dangerous mistake in this process. Never use a blowtorch, propane heater, or any open flame to thaw a pipe. Pipes are often run near wood framing, insulation, and other flammable materials, and an open flame in a confined space like a crawlspace or wall cavity is a genuine fire hazard, not to mention that direct flame can overheat and damage the pipe itself.
Step 5: Watch for signs of a hidden burst
Here's the uncomfortable truth about frozen pipes: sometimes the pipe has already cracked or split from the pressure of the ice, and you just haven't seen water yet because the ice blockage is still plugging the gap. As you thaw the pipe, keep an eye (and an ear) out for:
- Water appearing somewhere other than the faucet you opened
- A hissing sound as pressure releases
- Water pooling in an unexpected spot, like a ceiling below the pipe
If you notice any of these, stop applying heat immediately and shut off the water at the main valve.
When to stop and call in help
If you can't locate the frozen section, if it's buried inside a wall or ceiling where you can't safely access it, or if you suspect the pipe has already burst, this is where DIY needs to end. A hidden burst pipe can release a shocking amount of water in a short time once it fully thaws.
If you're not confident locating or thawing a frozen pipe on your own, or if you've found signs the pipe may already be damaged, call ProFlow Plumbing at (555) 010-4477. We'd rather help you thaw a pipe carefully than help you clean up after one that burst.