Homeowners in Illinois often tackle minor fixes like unclogging a drain or replacing a faucet. But not all plumbing work is a good DIY project—especially when it involves pressurized lines, gas systems, or work governed by state and local code.

Below are the types of plumbing jobs you should never DIY, along with what to do instead.

1) Any work on sewer lines or main cleanouts

Trying to repair or replace sewer piping—particularly anything connected to the main line—can create costly leaks, backups, and sanitation hazards. Sewer issues also can require specialized inspection equipment, permits, or coordinated work with city utilities depending on where the line runs.

If you’re dealing with repeated clogs, slow drains across multiple fixtures, gurgling sounds, or sewage odors, a licensed plumber can diagnose the cause and determine whether the problem is inside the home, in the building line, or further out.

2) Water heater replacement, gas piping, or venting changes

Water heaters involve high temperatures and, in many homes, combustion and venting systems. Improper installation or venting can cause carbon monoxide hazards. Changing gas piping—or modifying connectors, shutoff valves, regulators, or vent routes—is not a “small tweak” DIY job.

In Illinois, hiring a qualified professional helps ensure the work is installed to code and tested for safe operation. If your water heater is leaking, failing repeatedly, or you suspect venting problems, stop using it (when appropriate) and call a licensed contractor.

3) Repairs to pressurized supply lines behind walls

DIY plumbing is most dangerous when it moves behind finished walls or floors where a mistake won’t be immediately obvious. Cutting into supply lines that carry pressurized water can lead to rapid flooding, mold growth, and structural damage.

Jobs such as replacing sections of supply piping, re-routing lines, or repairing hidden leaks generally require controlled access, proper materials, and pressure testing—plus cleanup planning to limit downstream damage.

4) Anything involving backflow prevention or cross-connection risk

Backflow prevention devices are designed to stop contaminated water from flowing back into the potable (drinking) supply. Installing, testing, or repairing backflow prevention equipment should be handled by qualified professionals because incorrect setup can create public health risk—and many jurisdictions require regular testing.

If you have irrigation, a boiler system, a commercial connection, or any setup that could allow contamination backflow, ask your plumber about the correct device for your system and the required testing cadence.

5) Gas plumbing work (including connectors and shutoffs)

Even “minor” gas-related plumbing tasks—like replacing a gas shutoff, adjusting a connector, or relocating a gas line—carry real safety risks. Gas leaks can be difficult to detect and can lead to explosions or fires.

If you smell gas, leave the area, avoid switches/open flames, and follow local emergency guidance. For repairs, use a licensed professional familiar with gas system codes and safe leak-check procedures.

What to do instead: how to choose the right pro

When plumbing work crosses into code-heavy territory, the safest path is to hire a licensed plumber or the appropriate licensed contractor. Before work starts, ask about diagnosis, permits (if needed), warranty coverage, and how they’ll protect your home during the repair.

For many Illinois homeowners, the money you save on DIY can be outweighed by the cost of water damage, repeat repairs, or compliance problems. When in doubt—especially with gas, sewer, hidden leaks, or venting—pause and call a professional.