Water Heater Relief Valve Discharge Pipe: What It Means on Your Home Inspection Report

Every tank water heater has a temperature and pressure (T&P) relief valve: the valve with a lever on the top or side of the tank. If the water inside gets too hot or the pressure too high, it opens and lets water out. A.O. Smith states its purpose plainly: "to prevent excessive temperatures and pressures in the storage tank." Its manual puts the valve under an explosion hazard warning: "Overheated water can cause water tank explosion," and a properly sized relief valve "must be installed in opening provided." The water the valve releases can be scalding, and the discharge pipe carries it down toward the floor or a drain, away from people.

Your inspector found a problem with that pipe: it's missing, ends too high, is capped or plugged, has a threaded end, or is smaller than the valve's outlet. Each breaks a rule in the makers' own instructions. Under the InterNACHI standards of practice, inspectors look at the valve but aren't required to operate it.

Why It Matters

A capped, plugged, or undersized pipe can keep the valve from doing its job. A.O. Smith's manual labels this an explosion hazard: "Do not plug, block, or cap the discharge line. Failure to follow this warning can result in excessive tank pressure, serious injury or death." It adds that the discharge opening "must not be blocked or reduced in size under any circumstances," and that a run over 30 feet or with more than four elbows can restrict the valve's capacity. Bradford White's manual says "DO NOT thread, plug or cap the discharge line."

A missing or short pipe puts scalding water where people stand. Water released from the valve may be "extremely hot," A.O. Smith warns, and its manual carries a DANGER label: burn hazard, keep clear of the discharge. Rheem says to pipe the valve to a suitable drain so the water can't reach people or live electrical parts. A.O. Smith's manual warns that water over 125°F "can cause severe burns instantly resulting in severe injury or death," and the CPSC says water at 140°F causes third-degree burns in six seconds.

What the three makers' manuals require of the pipe:

• Full size the whole way. No smaller than the valve's outlet, with no reducing fittings (A.O. Smith, Rheem).
• Open at the end. Never capped, plugged, or blocked, with no shutoff valve between the tank and the relief valve (all three) or in the pipe itself (A.O. Smith, Rheem). Rheem and Bradford White add that the end must not be threaded.
• Ending low. Within 6 inches above an adequate floor drain or outside the building (A.O. Smith), or within 6 inches above the floor or anywhere below it (Bradford White), and never where the water can reach live electrical parts.
• Draining downhill. Pitched down so the valve and pipe drain completely, and protected from freezing (Rheem, Bradford White).
• Rated for the heat. Pipe approved for hot water (Rheem); A.O. Smith specifies pipe that withstands 250°F without distortion.

Local codes may add rules of their own; a licensed plumber knows what yours require.

What to Do Before Closing

• Ask the inspector which defect it is and for a photo, and whether there were signs the valve has been releasing water.
• Have a licensed plumber evaluate it. If the valve has been releasing water, the plumber should find out why: Bradford White and Rheem say it may be thermal expansion in a closed water system, which Rheem notes a new relief valve won't correct.
• Talk to your real estate agent about asking the seller to correct it or offer a credit within your inspection contingency.
• Don't test the valve yourself until the pipe is right. Lifting the lever releases hot water under pressure.

What to Do After You Move In

If it wasn't corrected before closing, have a licensed plumber install a discharge pipe that meets the manual and your local code. Until then:

• Keep people, especially children, clear of the valve outlet, and don't block it.
• Never cap or plug a valve that drips. A drip may be thermal expansion, which Bradford White and Rheem name as a possible cause, and either way it's a job for a plumber; our water heater leak guide explains the usual cause.
• Keep the heater at 120°F, the setting the CPSC urges to prevent scalds; A.O. Smith and Bradford White mark or preset their controls at about that. On an electric heater, adjust the thermostat only with the breaker off.
• Put a leak alarm at the base of the tank to catch a weeping valve or tank early; see our leak alarm guide.

Once the pipe is right, test the valve yearly as all three makers recommend; our flush guide covers the precautions. If it doesn't reset and keeps releasing water after a test, A.O. Smith says to immediately close the cold water inlet and replace the valve, a plumber's job.

Can You Fix It Yourself?

No. The valve and its pipe are code-required safety equipment, and Bradford White recommends that its heaters be installed and serviced by a plumbing professional. Your part: keep the area clear, keep the heater at 120°F, and never cap a drip.

Frequently Asked Questions

Is a missing T&P discharge pipe a code violation?

It breaks the manufacturers' installation instructions, which all call for a discharge line run to a suitable drain or near the floor. Local codes add their own requirements; a licensed plumber can tell you what your jurisdiction requires.

Can I cap a dripping relief valve?

Never. All three makers forbid plugging or capping the valve or its pipe. Periodic discharge may be due to thermal expansion, Bradford White and Rheem say, and Rheem's suggested fix is an expansion tank on the cold water line, installed by a plumber.

Can the discharge pipe be PVC?

Only pipe rated for the job. Rheem calls for pipe approved for hot water distribution, A.O. Smith requires pipe that withstands 250°F without distortion, and local code decides which materials qualify.

The Bottom Line

The relief valve is what stands between overheated water and what A.O. Smith calls a "water tank explosion," and its pipe sends the scalding water it releases down toward the floor, away from people. A capped, plugged, or undersized pipe can choke the valve; a missing or short one can spray scalding water. Have a licensed plumber correct it, keep the heater at 120°F, and never cap a drip. See more findings in our inspection report decoder.

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