A temperature and pressure relief valve that drips is opening, and the useful question is what is making it open. One manufacturer’s residential electric water heater manual says a valve that “weeps or discharges periodically” may be responding to thermal expansion in the water supply, and tells the owner to consult a local plumbing contractor or the water utility. The same manual says, in the same breath, not to plug the valve. This page sets out what that manual and an A. O. Smith technical bulletin say, and where they stop.
What The T&P Valve Is
The T&P valve is the safety device that releases water when a tank gets too hot or too pressurised. State Water Heaters’ residential electric manual (part 0002917490-0) describes a combination temperature-pressure relief valve certified to ANSI Z21.22 and the code requirements of ASME, marked with a maximum set pressure not exceeding the heater’s marked working pressure, which that manual gives as 150 pounds per square inch for the heater it covers. Other makers and models publish their own figures, so treat that number as one manual’s, not a universal one.
The same manual is specific about the discharge pipe. Any discharge must exit within 6 inches above, or at any distance below, the structural floor, and must not be able to contact a live electrical part. The discharge opening “must not be blocked or reduced in size under any circumstances,” and the pipe “must not be plugged or blocked.” That is why a pipe ending near the floor with water at its end is a valve discharging, not a mystery leak.
Why A T&P Valve Drips Periodically
The first cause both manufacturers name is thermal expansion in a closed water system. The manual says that if the valve “weeps or discharges periodically, this may be due to thermal expansion,” and notes the heater may have a check valve in the water line or a water meter with a check valve. It then says to consult a local plumbing contractor and/or the local water utility, and not to plug the valve.
A. O. Smith’s Technical Bulletin 45 describes how that looks in a house. Its listed symptoms include a relief valve that drips during any recovery cycle when no hot or cold water is being used, hot water pipes that creak while the heater recovers with all valves closed, and faucets that drip during a recovery cycle. Its explanation is that water expands when heated, that water will not compress, and that check valves at the meter, pressure reducing valves that also act as check valves, and water softeners acting as backflow preventers can each leave the system with nowhere for that expansion to go.
The State manual is blunt about what follows. The valve “is not intended for the constant relief of thermal expansion,” and constant relief is called “an unacceptable condition” that “must be corrected.” The A. O. Smith bulletin says the same from another angle: “do not depend on the T&P valve to handle thermal expansion,” because the valve was designed as an emergency relief device only and could be subject to reduced effectiveness or failure. The correction both point to is a provision for expansion, which is the subject of our expansion tank guide.
Valve dripping and you are not sure why? Call (717) 500-8528 and describe when it drips.
Other Causes The Manual Names
A dripping valve is not always an expansion problem, and the manual lists the alternatives itself. Its troubleshooting notes say small amounts of water from the valve “may be due to thermal expansion or high water pressure in your area,” and that the valve “may be leaking at the tank fitting.” It also says water in the bottom of the heater or on the floor may come from condensation, loose connections or the relief valve, and instructs: do not replace the water heater until a full inspection of all possible water sources is made. The table below lines these up.
| Named cause | What the documents say | Who it points to |
|---|---|---|
| Thermal expansion in a closed system | Valve weeps or discharges periodically; drips during recovery | Plumbing contractor or water utility; expansion provision |
| High water pressure | Small amounts of water may come from the valve | Bulletin 45 points to a pressure reducing valve where supply pressure is above 60 to 70 psi |
| Leak at the valve’s tank fitting | The valve may be leaking where it meets the tank | A technician |
| Something else entirely | Condensation, loose connections or the valve can all put water on the floor | Full inspection before any replacement decision |
If the water is arriving somewhere other than the discharge pipe, start with why a water heater leaks and leaking from the bottom, which work through the other sources.
The Annual Test, And Why This Page Does Not Walk You Through It
The manual says the valve must be manually operated at least once a year, and attaches a warning that matters more than the instruction. Nobody should stand in front of or around the discharge outlet, and the water “may be extremely hot.” If after manual operation the valve fails to reset completely and keeps releasing water, the manual says to close the cold water inlet to the heater immediately, follow the draining instructions, and replace the valve with a new one.
We are reporting that warning, not recommending that a homeowner stand next to a pressurised valve and open it. Hot water, a pressurised tank and a valve that may not close again is a combination to hand to a technician, which is also why we give no step-by-step here.
If It Will Not Stop Releasing Water
Closing the cold water inlet is the manual’s instruction for a valve that keeps releasing water after it has been operated. Energy shut-off differs between gas and electric units, and a gas odor changes the whole procedure, so use our emergency shut-off guide rather than improvising. Then call. Our emergency water heater repair page covers urgent calls, and water heater repair in Lancaster, PA covers the rest.
What This Page Will Not Tell You
It will not tell you your home’s water pressure, the failure rate of these valves, or what a replacement costs. Your pressure is a measurement taken at your house. We found no published failure rate that applies to this site’s service area, and no published price for replacing a relief valve that we can cite, so none is given. We also say nothing about which devices any Pennsylvania or Lancaster-area municipality has a rule about, because we have not located a rule we can quote. For the cost of what usually sits behind a repair, see the water heater repair cost guide, and for the larger decision, repair or replace.
Relief Valve Will Not Stop Releasing Water?
Service requests and emergency service are available 24/7 across Lancaster City and Lancaster County.
Call For Emergency ServiceT&P Relief Valve FAQ
Is it normal for a T&P relief valve to drip?
The manufacturer documents we read treat periodic dripping as a condition to be corrected, not a normal state. State Water Heaters’ electric manual says a valve that weeps or discharges periodically may be responding to thermal expansion, and that the valve “is not intended for the constant relief of thermal expansion.” Who should look at it, and what they will find, depends on the property.
Can I cap or plug the T&P discharge pipe to stop the drip?
No. The State Water Heaters manual says the discharge opening must not be blocked or reduced in size under any circumstances, that the pipe must not be plugged, and it says not to plug the valve. A plugged valve cannot do the one job it exists for. Find the cause of the discharge instead.
Why does the valve drip only after the heater has been running?
Because the pattern A. O. Smith lists for thermal expansion is dripping during the recovery cycle. Technical Bulletin 45 describes a relief valve that drips during any recovery cycle when no hot or cold water is being used. That pattern points toward expansion, but it is a possible cause to be confirmed by someone measuring the system, not a diagnosis from a drip.
Does a dripping T&P valve mean I need a new water heater?
Not on the manual’s own wording. The State Water Heaters manual says not to replace the water heater until a full inspection of all possible water sources has been made and the necessary corrective steps taken, and it lists expansion, high pressure and a leak at the valve’s tank fitting among the causes of valve discharge. Our repair-or-replace guide covers the larger decision.
What should I do if the valve keeps releasing water?
The manual’s instruction is to close the cold water inlet to the heater immediately. Energy shut-off depends on whether the unit is gas or electric, and a gas odor changes the procedure entirely, so follow our shut-off guide and then call for service.
Who looks at a leaking T&P valve near me in Lancaster County?
Lancaster Water Heater Pros services water heaters across Lancaster City and Lancaster County. Describe when the valve drips and whether the unit is gas or electric when you call (717) 500-8528. Service requests are accepted 24/7.