Some plumbing problems are simple enough that folks confident doing DIY work will be happy to tackle. Other issues, though, can present major challenges even to people with experience. It's wise to know when to say enough is enough and bring in a professional so let's take a look at three times when that may be the case.
The Issue Won't Quit
Dealing with something like a simple toilet repair to the order of replacing the chain on a ball-and-cock system is a job many DIYers are willing to tackle. If you keep running into the same problem with the same systems, however, it may be time to get professional help. For example, if a toilet starts developing slow draining issues after you've fixed it a couple of times, the issue may require a more advanced teardown than you'd expect. Don't keep fighting with equipment to save a buck, especially if that money is going down the drain literally in the form of your water and sewer bills.
Anything Attached to Gas or Electrical Systems
The classic version of this problem is performing a water heater installation. Even if you're licensed to deal with electrical work, it's probably best to leave the job to someone who has experience dealing with water and electricity issues in the same environment. This is the sort of work that needs to be done the right way the first to prevent safety problems so get someone qualified involved.
Similar logic applies in situations where things have gone badly. If there's flooding in your basement and water is near the electrical box, for example, you're probably better off having both utility providers turn things off than risking your life messing with the problem. Once that's under control, get licensed professionals to deal with the separate issue. Make sure you do a good job of coordinating their efforts.
Near Main Water Lines
In most areas, fiddling with the main water lines is downright illegal. A licensed professional is required to handle the work, and you'll most likely also have to inform the utility company that you're planning such work. They'll have to send someone out to shut things off, and they'll have to do the same thing when you need to have the system repressurized.
If you're unsure what components belong to the water company, look for tags, large valves, and gauges on pipes coming out of the walls, especially in the basement. When you see any of those elements near a line, assume it's something you shouldn't touch.