Kudos to all you DIY-ers who confidently clean the showerhead to improve your water pressure, tighten the trap under the sink to fix a leak, and even replace that old bathroom sink. We applaud you! Sometimes however, repairs or installations call for an experienced plumber with professional training and knowledge of the most recent coding standards.

Here are a few instances when you should drop that wrench and call a professional!

There’s no water available. If no water is flowing from your faucets, you have a serious plumbing problem. The most likely causes are either a blockage or a leak somewhere in the lines. Since most of your pipes are concealed in your walls or under your house, you need a plumber to diagnose and quickly correct the problem.

You have no hot water. Unless your tank is leaking, you know there’s no hot water because the darn thing has stopped working. The question is why. It can take time and patience to find the answer, and is always best left to a professional. If you have an electric tank, you may be looking at a bad heating element, a tripped circuit breaker or blown fuse, a faulty thermostat, or a bad overload switch. Gas heaters have thermocouple burners and igniters that can fail. Your plumber will be able to tell you if your tank can be repaired or if you need a new one. If the verdict is a new hot water heater, your plumber will make it an easy process by hooking up the new one, testing to be sure it’s working properly, and disposing of the old tank.

You’re installing new appliances. When remodeling your kitchen, bathroom, or laundry room, it can be tempting to cut costs by trying to install appliances on your own. A word to the wise—the installation process is more complex than it might seem. New installations can affect your overall plumbing system, including drains and supply lines. In order to keep all systems running smoothly, rely on your plumber to do the job right.

You have a blocked sewer line. Usually, a stopped up toilet or slow-draining sink is easily remedied. If you’ve tried all the tricks you know and your system is still backed up, you most likely have a bad blockage in the line that runs to the main sewer. Often this is caused by tree roots. It’s important to be aware that the sewer rodding machines you can rent to clear the line can damage your sewer! Call your plumber or a drain-cleaning service. They’ll do a professional job, and if any unavoidable damage occurs to your line, they will repair it.

Your toilet won’t stop running. This may seem like a small problem, and often creeps up on you a little at a time. Don’t let this go! Most likely the seal that connects the toilet tank to the bowl has been damaged, causing the tank to constantly fill. The sound of constantly running water can be annoying, but more importantly, if left unfixed, the leak will literally add hundreds of dollars to your yearly water bill.

Remember, there are some things you can guess your way through, but plumbing isn’t one of them. Know when to rely on your plumber for efficient, professional repairs and installations.