Pressure Relief Valve Service

Last updated September 24, 2026

The temperature and pressure relief valve, or T&P valve, is a safety device on virtually every tank water heater, and one that should never be capped, blocked or ignored.

What it's for

The T&P valve opens automatically to release pressure or temperature that exceeds a safe threshold inside the tank, preventing a dangerous buildup. It's a safety component, not an optional feature.

Why it should never be capped

Capping or plugging a T&P valve removes the one safety release the tank has if pressure or temperature climbs too high. This is not something to work around under any circumstance.

Signs it may need attention

Periodic dripping from the valve's discharge line, visible corrosion around the valve, or a valve that has never been tested are all reasons to have it looked at. Occasional dripping after the tank was recently used heavily can be normal; frequent or constant dripping usually is not.

What service involves

A technician tests the valve's operation, inspects it for corrosion or damage, and replaces it if it's not functioning correctly or is at the end of its service life.

What normal versus concerning dripping looks like

An occasional drop or two right after heavy hot water use can be within normal range for some systems. Frequent, ongoing dripping, especially without a recent heavy-use event, is the pattern worth having checked.

Why this valve is inspected, not adjusted, by a homeowner

T&P valves are calibrated safety devices; if one seems to be malfunctioning, the correct response is professional inspection and replacement if needed, not adjustment or bypassing.

Why It's Dripping in the First Place

A T&P valve that drips often isn't the real problem, it's frequently a missing or failed expansion tank failing to absorb pressure the way it should. Worth having both checked together.

What the Relief Valve Does

The temperature and pressure relief valve, often called the T&P valve, is the most important safety device on a water heater. It opens automatically if the water temperature reaches about 210°F or the pressure reaches about 150 psi, releasing water to prevent a tank rupture. A tank without a working relief valve can become dangerous if a thermostat fails.

Why Relief Valves Drip

A valve that drips occasionally after heating cycles is usually responding to thermal expansion in a closed system, not failing. An expansion tank fixes that. A valve that drips constantly may have debris or mineral scale on its seat. A valve that discharges large amounts of hot water indicates overheating or excessive pressure and needs immediate attention.

Testing the Valve

Lifting the valve's lever briefly should release a burst of water and then reseat. Test once a year. If it doesn't open, or doesn't stop dripping after testing, replace it. In Colorado's hard water, valves that are never tested can scale shut.

Discharge Pipe Requirements

The discharge pipe must be the full size of the valve outlet, run downward, end within about six inches of the floor or at an approved drain, and have no valves or caps. It shouldn't be threaded at the end. Many older Colorado installations have discharge pipes that end too high or into a bucket, which should be corrected.

Replacing a Relief Valve

Replacing the valve requires shutting off the water and power or gas, draining some water, unscrewing the old valve and installing a new one rated for the tank. The discharge pipe is reconnected, the tank refilled and the valve tested.

A Common Colorado Scenario

A homeowner in a 1990s Littleton or Aurora house notices a small puddle under the water heater's relief valve discharge pipe every evening. The tank is only six years old. The cause is almost always thermal expansion: the city installed a pressure-reducing valve at the meter, turning the home's plumbing into a closed system, and every time the water heater runs, pressure climbs until the relief valve lets a little water out. Replacing the relief valve won't fix it; adding a properly charged expansion tank will. Measuring the home's static pressure first also matters, since a failed pressure-reducing valve can let street pressure exceed 80 psi, which is too high for household plumbing.

How Hard Water Affects Relief Valves

In Colorado's hard water, mineral scale can build on the relief valve's seat and stem, especially if the valve is never tested. A scaled valve may drip constantly after it's finally opened, or it may not open at all when needed. Testing the valve once a year keeps it moving freely. If it drips after testing, it should be replaced, and the cause of any scaling, such as high tank temperature, addressed.

What Never to Do

Never cap, plug or remove a relief valve, and never install a valve in its discharge line. A tank without a working relief path can overheat and rupture violently if a thermostat or gas control fails. If a relief valve is causing a nuisance drip, the fix is to address pressure or replace the valve, not to disable it.

Questions Homeowners Ask

How long does a relief valve last? Many manufacturers suggest replacement every few years or when the water heater is replaced, since valves can scale or corrode.

Is it normal for the valve to release water when I test it? Yes; it should release a burst and then reseat.

Why is my discharge pipe hot? Hot water is escaping through the valve, which suggests overheating or high pressure; turn off the heater and call.

Can a relief valve drip because of high city pressure? Yes; a pressure-reducing valve set too high or failing can cause it.

Temperature Settings and Relief Valves

A tank set very hot, above 140°F, is closer to the relief valve's temperature trigger and scales faster. Keeping the setpoint around 120°F reduces both risks.

Relief Valves on Tankless and Boilers

Tankless heaters and boilers also have relief valves, rated for their own pressures. They need the same testing and discharge piping.

Relief Valve Discharges in Colorado Homes

In many Colorado homes, relief valve discharge pipes are routed to floor drains, drain pans or outside walls. A discharge that goes outside can freeze in winter, which is one reason codes require the line to end near the floor indoors or at an approved location. A pipe that discharges onto a finished floor or behind a wall where leaks go unnoticed should be rerouted. When a discharge happens, hot water can cause burns, so the end of the pipe should never point toward where people walk.

Replacing a Relief Valve on an Older Tank

On an older tank, a stuck or corroded relief valve may be hard to remove, and the fitting can be fragile. If the tank is near the end of its life, replacing the whole unit may be wiser.

Where the Discharge Pipe Should Go

The relief valve's discharge pipe should run full size, without valves or threads at the end, to within about 6 inches of the floor or to an approved drain, so any release is visible and can't spray someone. A capped or undersized pipe is a safety defect.