If a soldered joint is overheated, _______.

When a soldered joint is overheated, several negative effects can occur, including the burning of flux, distortion of the joint, and swelling.

The flux used in soldering serves as a cleaning agent and helps to improve the flow of solder by preventing oxidation. Overheating can lead to the burning of the flux, making it ineffective. An ineffective flux can compromise the quality of the joint, resulting in poor solder adhesion.

In addition to the burning of flux, overheating can cause the joint itself to distort. High temperatures can alter the shape and fit of the piping components, leading to improper alignment or a weak joint. A distorted joint might not seal correctly, increasing the likelihood of leaks.

Swelling can also occur in the materials being joined due to the extreme heat. This physical change in size can further stress the joint and potentially lead to failure.

Therefore, when all these factors are taken into account, it's clear that overheating a soldered joint results in multiple adverse effects, thus making the option that states "All of the above" the most comprehensive and correct answer.