What should be done if a plumbing pipe freezes?

If a plumbing pipe freezes, applying a heat source gradually is the recommended action because it allows for a controlled thawing process. Gradual application of heat helps to prevent the pipe from expanding too quickly, which could potentially lead to the pipe bursting. This can be done using heating pads, hair dryers, or towels soaked in hot water.

Using a heat source also allows you to keep an eye on the thawing process. It is essential to start from the section of the pipe closest to the faucet and work your way back, as this helps to relieve any pressure build-up that may have occurred from the ice blockage.

Other options may lead to damage or leave the issue unresolved. For instance, leaving a frozen pipe alone could lead to a burst pipe as the ice continues to expand with pressure. Filling it with hot water isn't effective because it can cause uneven heating and stress on the pipe. Breaking the pipe to relieve pressure is a drastic measure that can lead to extensive repairs and flooding, making it an undesirable solution.