Top 10 Most Common Plumbing Issues

Leaking pipes – this is by far the most common plumbing issue that home inspectors run across on a regular basis whether we’re talking about supply or drain pipes. Many home owners don’t regularly check their plumbing, such as below their bathroom and kitchen sinks, so small “drip-drip” leaks can lead to bigger issues such as water damage, rot, and mold if these small leaks aren’t caught early. I include regularly checking under sinks as a preventive maintenance suggestion in my inspection reports. Below, there is a small leak just shy of where the drain pipe enters the wall.
Improperly pitched drains – drain pipes need gravity to properly empty of water towards the sewer source. Standard practice calls for drain pipes to have ¼” per foot pitch although 1/3” per foot is allowed if the drain pipe is 3” diameter or larger. Improper pitch can allow for leaks and/or a slow draining of a sink or bathtub.
Corrugated drain pipes – corrugated drain pipes are sold at many hardware stores, so home owners assume these are a good repair method. I often find these under a kitchen or bathroom sink that a home owner (or anyone but a non-licensed plumber) installed. Plumbing standards forbid them because they tend to allow for clogging and are difficult to clean. Drain pipes must be smooth interior walled, and corrugated drain pipes are anything but.
Water heater T&P valves lacking a proper discharge pipe – All modern water heaters are required to have a temperature & pressure (T&P) relief valve and a proper discharge pipe connected to this valve. This valve opens in case the pressure or temperature gets too high inside the water heater tank. The water heater is a pressure vessel which could explode or go shooting up through the home if there was a malfunction; the relief valve helps prevent this from happening. Without a proper discharge pipe, if the valve were to open, someone standing nearby could get scalded. The valve must have a discharge pipe that meets a few criteria: (1.) the pipe must be hot water rated, meaning almost all plumbing types are permitted except for PVC and ABS; (2.) the pipe should terminate to a visible area approx. 6” above the floor adjacent to the water heater; (3.) the bottom of this pipe should not be threaded (which can prevent someone from possibly capping this pipe); (4.) the diameter of the discharge pipe should be the same diameter as the T&P valve (normally ¾”). Read my article on the topic.
Water Heater Temperature Set Too High – Hot water in the home should not exceed 120° F or else a scalding hazard can exist. It only takes 4~6 seconds of 140° F hot water contacting human skin to lead to 2^nd or 3^rd degree burns (the worse type of skin burns). Modern gas and electric water heaters have temperature settings to control the output hot water. Gas water heaters normally have a dial on the front and electric water heaters have settings at each heating element. Hot water over 120° F can also waste energy as the water heater needs to try to maintain whatever temperature it is set to. Boilers can also serve the purpose of heating the home’s potable water; a mixing valve can be installed on a boiler that is set up in this fashion. A mixing (aka ‘tempering’) valve adds small amounts of cold water to the hot potable water supply line to help prevent potable hot water from becoming dangerously hot. The photo below shows a laser thermometer measuring hot water at a kitchen sink. As you can see, the measured temperature was 137.5° F which can scald.
Missing Traps – all plumbing fixtures (other than toilets) require a trap in their drain pipe. Toilets have a trap incorporated into their design. A trap helps prevent sewer gases (and “vermin”) from possibly entering the home through the drain pipes. I will often see a laundry drain, for example, that someone installed themselves that has no trap installed. This sometimes becomes very evident when you stand near the drain and smell sewer gases. Often times, like in the photo below, I see a dishwasher connected to a drain pipe under the sink and the connection is downstream of the sink’s trap. Sewer gas entry may occur into the home through the dishwasher in this case. The drain connection should have been made upstream of the trap instead of it’s current location. Also, drain lines should have only 1 trap installed; having two traps installed in series can allow for clogs. The photo below shows a dishwasher drain hose directly connected to a sink drain line downstream of the trap. This connection needs to be made upstream (above) the trap to prevent sewer gases from entering the home through the dishwasher.
Slow Drains – this has been a common issue since plumbing was first installed in homes and, in most cases, isn’t difficult to address. This often is caused by a hair clog in a sink or bathtub drain or a clogged toilet and each can often be addressed with a little plunger work. Using drain clearing chemicals is not recommended as these chemicals could splash back and may burn or blind you. In some cases, especially in older homes, a slow drain can be related to a broken or partially blocked main sewer line in the yard. Older drain pipes (clay or cast iron) may have separated over time or have tree roots growing into them. Determining this would most often require a licensed plumber to snake the line to find the issue buried underground.
Loose and/or Leaking Toilet – this is an issue that I run across on a regular basis. Over time, toilets can come loose from the bathroom floor. Once it happens, the seal between the toilet and the drain pipe/floor is compromised and this can allow for leakage resulting in subfloor damage. Sometimes this water also then leaks into the ceiling below the toilet which can also result in mold. A little gentle rocking of the toilet will determine if the toilet is loose. To find moisture within the bathroom floor, home inspectors use a moisture meter around the base of the toilet’s perimeter. Even if you don’t see discolored flooring around the toilet, the moisture meter can find moisture within the subflooring. A repair may entail simply reseating the toilet with a new wax ring. If evidence of moisture is found (either with a moisture meter or visible staining), further evaluation for possible hidden damage (subfloor rot, mold, etc.) is warranted prior to reseating the toilet with a new wax ring.
Dishwasher Drain Hoses – All dishwasher manufacturers list the need for either a drain line high loop or an air gap in their installation instructions. Air gaps are rarely seen in the eastern US so high loops are the predominant method to be used. Whether the drain discharges into a kitchen sink drain or garbage disposal, the high loop helps prevent dirty contaminated water from the sink drain from possibly getting back into the dishwasher and contaminating its supposedly ‘clean and sanitary’ contents. Read my Improperly Installed Dishwasher Drains: A Very Common Defect article.
Drain Stoppers No Longer Functioning – I find this issue in bathtubs in both older and fairly new homes. The older types of drain stoppers use a chain system to stop the flow of water from the drain when the lever is engaged. Sometimes, one or more parts of this chain system come apart over time and sometimes the actual lever gets stuck and can’t be moved out of position. A licensed plumber should be called in to make needed repairs. If a drain won’t stop, it can limit use of that sink or bathtub. In newer bathtubs, toe-tapper drain stoppers are very common. Over time, the spring inside this type of stopper can wear out or get damaged. Most hardware stores sell replacement top-tapper stoppers and replacing them is an easy chore.
© 2023 Matthew Steger
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Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at matthew@thehomeinspectorsnotebook.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.