The plumbing system serves a vital role: it brings water into the home and removes sewage. Common plumbing defects can cause moisture issues including rot, mold, and mildew. A faulty system can also allow dangerous sewer gases into the home.  Carefully checking the plumbing system is part of every thorough home inspection. During every Angel Home Inspection, we visually check all accessible piping and fixtures.  Whether you’re buying a new home or getting ready to list your home for sale, the following are the three most common plumbing defects we encounter.

Outdated Drain “S-Traps” Under Sinks

Differences between s-traps and p-traps

The most common plumbing defect we see are the use of “s-traps” under sinks. During home inspections, we must mark the existence of s-traps as a defect. The purpose of drain traps are to prevent poisonous sewer gases from entering a home.  The original style s-traps were marginally effective. Unfortunately, time and experience have shown that the water can be sucked out of an s-trap, leaving it dry and allowing sewer gases into the home. The most likely cause is when a bathtub or washing machine drains sending a gush of water through the plumbing. This surge creates a suction which can siphon the water out of other drain traps.   As a result, p-traps were developed. The primary difference is that p-traps have a horizontal run after the trap.  This design functions significantly better.  Installing p-traps under sinks is the best practice now.  Of course, even p-traps have installation specifications. If in doubt, contact a licensed plumber or Angel Home Inspections.

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Missing Water Heater Discharge Pipe

A copper water heater discharge pipe

Every modern water heater is equipped with a temperature/pressure-relief or TPR valve to prevent excessive water temperature and pressure.  Simply stated, TPR valves are safety devices designed to automatically release water in the event that pressure or temperature in the water tank exceeds safe levels. Without a TPR valve,  a water heater is effectively a potential bomb.  Water expands as it is heated. If the water heater malfunctions and gets stuck in heating mode, water in the system may become super heated (exceeding the boiling point). In such a case, the water pressure inside a water heater can build until the heater literally explodes.  The TPR is set to automatically open at a certain temperature or pressure to prevent the explosion.  When the TPR opens, both super hot water and/or steam will be released.  In combination with the higher pressure, this super hot water and steam can severely burn anyone nearby.  That is why every residential water heater must have a discharge pipe connected to the TPR valve. The discharge pipe directs the escaping water and steam downward releasing it within six inches of the floor or ground.

Discharge pipes must meet several specifications as to length, pipe material, and routing.   Generally, a copper discharge pipe is the best choice.  PVC should not be used as it can melt from excessive heat.

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Dishwasher Drain Connected Incorrectly

Two methods for dishwasher drain high loop installation

The last of the three most common plumbing defects is incorrectly installed dishwasher drain lines.  The two primary concerns are the “high loop” and the drain line’s connection points. When installing a dishwasher, the drain line must have a high loop before connecting to the home’s drain piping. The high loop serves two purposes. It ensures proper drainage of waste water during the drain cycle and prevents siphoning. The high loop also helps prevent contaminated water from the garbage disposal or sink drain from back-flowing into the dishwasher. There are a couple of options to install the high loop. The specifications vary in different areas of the country.  Some require an air admittance valve and some do not. 

Of equal or more important consideration is the connection point between the dishwasher’s drain line and the home’s drain plumbing pipe.  The dishwasher drain line must connect BEFORE the drain trap to prevent sewer gases from entering the home’s living areas.  Dishwasher drain lines connected below the sink’s drain trap are always marked as a plumbing defect. 

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Conclusion