Water Heater Relief Valve Leaking
Drip timing, supply pressure and tank temperature sort the causes.
By Jonathan West · reviewed 2026-10-28 ·how we research these
A water heater relief valve leaking only while the tank heats usually points to thermal expansion in a closed plumbing system. The fix is an expansion tank on the cold supply, and a new valve does not fix it. A drip that runs constantly points to high supply pressure, a worn or debris-fouled valve seat, or an overheating tank. That case needs a pressure reading and a licensed plumber.
The valve is a temperature and pressure (T&P) relief valve. It sits near the top of a storage water heater, with a discharge pipe running down toward the floor. It opens if the water exceeds roughly 210 degrees Fahrenheit or 150 pounds per square inch (psi). A discharging valve is generally doing its job. The danger comes from a blocked valve, which cannot protect the tank, and from water in the discharge pipe that can be scalding hot.
At DIY Repair Guide, we compiled the guidance below from the Building America Solution Center (BASC), a US Department of Energy (DOE) resource, and from general plumbing practice. We did not test these repairs. The symptom table below is compiled here from those sources.
Constant Drip or Drip Only While Heating
A drip that appears only while the tank heats, then stops when the tank is idle, points to thermal expansion.
A drip that runs constantly points to high supply pressure, a worn or debris-fouled valve seat, or an overheating tank. Timing alone cannot tell those three causes apart. A pressure reading and the temperature of the discharge pipe can.
A discharge pipe that is hot to the touch with a steady flow, a rumbling tank, or steam means the tank may be overheating. Shut off the power or gas supply at the heater's own control or shutoff, then call a licensed plumber right away.
Thermal Expansion in a Closed System
Thermal expansion is the most common cause of a valve that drips while the tank heats.
Heated water expands. In a closed plumbing system, meaning one with a check valve, a pressure-reducing valve (PRV) or a backflow preventer on the incoming main, that water has nowhere to go. Pressure climbs until the valve lifts and lets water out through the discharge pipe.
The repair is a thermal expansion tank on the cold supply. A new relief valve leaves the expansion in place. The tank has an air charge set to match household pressure, and setting that charge is plumber work on a pressurized line.
High static pressure may also need a PRV, so a pressure reading belongs in this check too.
High Supply Pressure
Service water pressure entering a home should be regulated to a maximum of 60 psi, according to the Building America Solution Center.
The same guidance says most plumbing codes require a PRV where the supplied utility pressure exceeds 80 psi. Local plumbing code adoption and amendment vary, so the code in your area sets what applies to your house.
Excess pressure can rupture supply lines and washing machine hoses, leak water heaters, cause dripping faucets, damage fixtures, and make dishwashers and clothes washers louder. Regulating to the 60 psi target also lowers water use and extends fixture life.
On a municipal supply, a PRV is typically a bell-shaped brass valve next to the main shutoff on the incoming service line. Many homes plumb outdoor hose bibs ahead of the PRV. A gauge on an outdoor tap can then read unregulated main pressure instead of the pressure the house sees. Private wells regulate pressure with a pump, a pressure switch and a bladder tank, and they do not use a PRV.
To read supply pressure, screw a hose-thread pressure gauge onto a tap on the house side of any PRV, such as a washing machine supply valve. A reading near or above 80 psi means pressure is the likely cause. A reading under 60 psi with a constant drip makes the valve itself or the tank temperature more likely. The figures compiled here do not cover readings from 60 to 80 psi, so check the water heater manual and local code for that range.
The high water pressure guide and the low water pressure guide cover those symptoms separately.
Worn Valve Seat and Debris
A worn or debris-fouled valve seat lets water seep past even when pressure is normal.
A constant drip with a gauge reading under 60 psi makes the valve itself or the tank temperature more likely. The reading decides between pressure and the valve before any part is replaced.
A gauge reading under 60 psi with a constant drip fits a seat problem, but it does not prove one, so a licensed plumber makes the call on replacement.
An Overheating Tank
A discharge pipe that is hot to the touch with a steady flow, a rumbling tank, or steam means the tank may be overheating.
Shut off the power or gas first, then call a licensed plumber.
Gas, venting, burner and live wiring work belong to a licensed plumber, heating, ventilation and air conditioning (HVAC) technician, or electrician.
Keep hands and face clear of the discharge pipe, since its water can be scalding hot. Shut off the power or gas at the heater's own control or shutoff, then call a licensed plumber right away. Do not try to restore service yourself.
Why You Never Cap the Discharge Pipe
The discharge pipe is never capped, plugged, threaded shut, or fitted with a valve.
A blocked relief valve cannot protect the tank, so the pipe stays open. The pipe runs down toward the floor, and its water can be scalding hot.
Capping the pipe hides the drip but leaves the tank without its relief. The water heater manual and local code govern the discharge pipe.
Never cap the discharge pipe, even to stop a drip. Keep hands and face clear of the water, which can be scalding hot.
Symptom-to-Cause Table
The table sorts each symptom to its likely cause and to who should do the work. It is compiled here from the cited sources and the general plumbing practice above.
| Symptom | Likely cause | First check | DIY or plumber |
|---|---|---|---|
| Drips only while the tank heats, stops when idle | Thermal expansion in a closed system | Note the drip timing and whether the system has a check valve, PRV or backflow preventer on the main | Plumber sets the expansion tank air charge |
| Constant drip, gauge reads near or above 80 psi | High supply pressure | Read supply pressure on a tap on the house side of the PRV | Licensed plumber |
| Constant drip, gauge reads under 60 psi | Worn or debris-fouled valve seat, or tank temperature | Note whether the discharge pipe runs hot | Licensed plumber replaces the valve |
| Constant drip, gauge reads 60 to 80 psi | Not covered by the figures compiled here | Read supply pressure | Licensed plumber |
| Hot discharge pipe with steady flow, rumbling, or steam | Possible overheating tank | Shut off power or gas at the heater's own control or shutoff | Call a licensed plumber right away |
| Still dripping after the valve is replaced | Valve venting excess pressure | Read supply pressure | Licensed plumber |
| Gas, venting, burner, or live wiring work | Outside homeowner scope | None | Licensed plumber, HVAC technician, or electrician |
Replace the Valve or Fix the Cause
Replacing a T&P valve typically costs $150 to $350 (typical United States (US) figures, for orientation only).
A licensed plumber replaces the valve.
Replacing the valve does not stop the drip when the valve is venting excess pressure. In that case the pressure in the system is the cause, and a new valve leaves it in place.
The cause decides the repair. Thermal expansion calls for an expansion tank on the cold supply, and high supply pressure may call for a PRV.
For replacement and repair costs, see the water heater replacement cost page and the water heater leak repair cost page. For a tank's age, see the water heater lifespan page. Other leak sources, such as fittings, the drain valve, the anode rod port, and the tank shell, are covered on the water heater leaking guide.
A drip that appears only while the tank heats is usually thermal expansion. An expansion tank on the cold supply fixes it. A constant drip needs a pressure reading and a licensed plumber. A hot discharge pipe with a steady flow, steam or a rumbling tank means shutting off power or gas at the heater and calling a licensed plumber right away. The answer changes if a constant drip comes with a gauge reading under 60 psi, because then the valve itself or the tank temperature is the likelier cause. Based on the BASC figures and the symptom table compiled here, start by timing the drip against the heating cycle, and if it runs constantly and the discharge pipe is not hot, read supply pressure with a gauge.
Common questions
How to make a pressure relief valve stop leaking?
It depends on the cause, and the drip timing sorts the cause first. A drip only while the tank heats is usually thermal expansion, and the repair is a thermal expansion tank on the cold supply, set by a licensed plumber. A constant drip needs a gauge reading: near or above 80 psi points to supply pressure, and under 60 psi points to the valve or the tank temperature. Replacing the valve alone does not stop a drip when the valve is venting excess pressure.
How much does it cost to replace a water heater pressure relief valve?
Replacing a T&P valve typically costs $150 to $350 (typical United States (US) figures, for orientation only). For plumber rates, see the plumber cost page.
What is a TPR valve?
A TPR valve is a temperature and pressure relief (TPR) valve, the same device as a T&P valve. It sits near the top of a storage water heater, with a discharge pipe running down toward the floor. It opens if the water exceeds roughly 210 degrees Fahrenheit or 150 psi.
How much water should come out of a hot water relief valve?
None of the sources used here gives a flow amount for a discharging valve. The drip pattern is the check to start with. A drip only while the tank heats fits thermal expansion. A constant drip calls for a pressure reading and a licensed plumber. A hot discharge pipe with steady flow, or steam, means shutting off power or gas at the heater and calling a licensed plumber right away.
Is it normal for a water heater to leak from a release valve?
A discharging T&P valve is generally doing its job, and the most common cause is thermal expansion in a closed plumbing system. A discharge that happens only while the tank heats fits that cause. A constant drip is a different case, and it can point to high supply pressure, a worn or debris-fouled valve seat, or an overheating tank.
What is the 3 rule for pressure relief valves?
We cannot source a single '3 rule' for pressure relief valves. The valve's rating and the local plumbing code govern what applies to your heater, and adoption and amendment of plumbing code vary by jurisdiction.