Temperature / Pressure Relief Valve Test Procedure

POST a QUESTION or COMMENT about test procedures for temperature / pressure relief valves on water heating equipment

Temperature / Pressure Relief Valve (TPR valve) or easing valve test procedures.

This article describes manufacturer and industry-recommended procedures and schedules for testing TPR valves.

We also discuss hazards associated with testing TPR valves and the hazards of a blocked or obstructed temperature/pressure relief valve test lever.

Page top photo: temperature/pressure relief valve on a residential steam bath generator.

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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Using the Temperature/Pressure Relief Valve Test Lever

A T&P valve (TPR valve or easing valve) is a critical safety devices used on water and steam heating equipment to prevent a dangerous BLEVE EXPLOSION. T&P valves are designed to open to relieve pressure and temperature in the heating equipment should either of those rise above an unsafe level.

For example on a residential water heater the TPR is typically set to open at a pressure of 150 psi or if the water temperature reaches 210°F. On older water heaters using older TPR valves you may find the valve rated to open at 125 psi.

[Click to enlarge any image]

In all events the opening pressure of a pressure or temperature relief valve should never exceed the working pressure of the tank - such a condition is unsafe and violates water heater warranties and plumbing codes.

An inspection of a T&P valve for its ability to perform safely includes a number of checkpoints such as looking for leaks, mechanical damage, blockage, or for a TPRV that is not properly sized or matched to the equipment it's supposed to protect.

We summarize those inspection points for water heaters

at RELIEF VALVE, WATER HEATER.

T&P valves for hydronic (hot water) and steam boilers are discussed separately

at RELIEF VALVE, TP VALVE, BOILER.

In our photo I'm pointing to the test lever on the temperature/pressure relief valve on a residential water heaters. These safety devices are required on all heated water or steam vessels or tanks and are found on both residential and commercial water heating equipment.

T&P Valve Test Procedure

Watch out: PRECAUTIONS MUST BE TAKEN TO AVOID PERSONAL INJURY FROM CONTACT WITH HOT WATER AND TO AVOID PROPERTY DAMAGE. - Watts (2011)

Typical and more-wordy warnings include

Before manually operating the relief valve, make certain no one will be exposed to the danger of the hot water released by the valve. The water may be hot enough to create a scald hazard. The water should be released into a suitable drain to prevent injury or property damage.

... Annually check the operation of the pressure-relief valve. Lifting the lever handle on the pressure-relief valve opens the valve to flush hot water through the discharge line to the drain.

After several gallons have drained, release the lever handle to close the valve and stop draining.

Illustration: typical parts of the operating mechanism of a relief valve, adapted from FlowStar Safety Relief valves cited below. Note that in this illustration the temperature sensing probe that would extend into the hot water from the valve base is not shown. Flowstar is a safety relief valve provider in the UK.

[Click to enlarge any image]

In this illustration key operating or moving parts of this relief valve are identified as (3) Lifting lever, (4) Spring, (6) Bonnet, (9) Disk, (12) Inlet body, (16) Spring Carrier, (17) Spindle or lifting rod operated by (3) the test lever.

In Australia and New Zealand the test lever on a temperature/pressure relief valve is called an easing lever but performs the same purpose.

5 Steps to Proper Safety Test of a TPR or Temperature/Pressure Relief Valve

Inspect the temperature-pressure valve

and the heater for safety before touching the valve.

Watch out: do not attempt to test the TPR valve if:

There is no discharge tube in place to divert hot water to a drain or other suitable location. You or a bystander could be sprayed with scalding water

There is visible damage, scale or clogging that leads to suspicion that the valve is already damaged or unsafe

It's a holiday (stores are closed) or a Sunday or late at night such that if the valve fails to close you will not be able to arrange prompt repairs, leaving the building and occupants with no hot water or no heat
Lift the test lever:

To test the valve the lever on the valve is lifted manually.

Typically you'll just lift the lever briefly- sufficient to see that water is discharged.
Observe the valve discharge:

lifting the test lever should result in (hot) water flushing through the valve and its discharge tube into a bucket placed below the discharge tube for that purpose or into a floor drain.
Release the relief valve test lever:

When you release the test lever the water flow should stop.

Release the test lever normally or even somewhat gently; don't pound, wiggle, twist or otherwise torture the relief valve.
Observe that water flow stops

at the valve discharge tube.

You may see a minute or so of dripping from the tube as residual water in the tube drains out but water flow and dripping should stop within a minute.

Besides testing the TPR valve, other water heater TPR valve inspection points

are given at RELIEF VALVE INSPECTION POINTS

... A new pressure-relief valve, complying with the Standard for Relief Valves and Automatic Gas Shut-Off Devices for Hot Water Supply Systems, ANSI Z21.22/CSA 4.4, must be installed at the HOT water outlet connection of the water heater during installation. Local codes shall govern the installation of any relief valves. -

TANKLESS WATER HEATER USE & CARE MANUAL [PDF] for Rheem®, RUUD®, Richmond®, Paloma®, and Sure Comfort® residential tankless water heaters.

After lifting the easing lever or relief valve opening lever, lower it gently back to its closed position. You can let the TPR valve "snap" closed on its own - as is recommended by typical water heater TPR valve instructions but Rheem points out [citation needed] that rough handling of the relief valve test lever, such as allowing it to "snap" closed, can damage the temperature and pressure relief valve - a dangerous condition that could lead to a water heater explosion

or BLEVE EXPLOSION.

OPINION: I think that the "snapping relief valve shut" problem is likely to occur principally when testing an old valve whose valve seat washer is already dry and brittle. Letting a newer valve (5 years old or less) test lever snap shut under control of the lever's own spring ought cause no damage.

If water does not flow freely when the temperature/pressure relief valve is opened, the valve should be replaced by a licensed plumber, making sure that an approved, properly-rated TP valve is installed.

If your temperature/pressure relief valve has not been tested or replaced sooner than five years, Rheem recommends that the TP valve should simply be replaced. More frequent replacement of the safety valve may be needed in areas where hard water is found.

Watch out: some of the TPR valve test procedures and articles we reviewed point out that testing the valve by operating it more often than recommended risks damaging the valve, causing leaks, and possibly making it unsafe.

See the additional T&P valve inspection points described

at RELIEF VALVE INSPECTION POINTS

What to Do If a T&P Valve Won't Shut Off

If the relief valve closes but continues to drip, you might be able to stop the drip by flushing the valve seat (lifting the test lever) a time or two.

When that does not work, try tapping gently on the center lift pin or rod to try to re-seat the valve washer. Don't bang the heck out of the valve or you may convert a small leak into a dangerous hot water catastrophe.

What if The TPR Valve Does Not Stop Flowing or Dripping?

Turn off the water heater or boiler
Turn off cold water supply into the water heater or boiler
If water continues to flow you may need to remove pressure from the hot water system or boiler; at a water heater this may be achieved by running hot water at nearby sinks or tubs
Clean up the spilled water
Explain & document that your test has disclosed an important safety and plumbing defect.

Considering the risks and costs of a bad T&P valve flooding a home at any time, particularly one that's in the process of being sold, at least some home inspectors will eschew actually testing the T&P valve by lifting the test lever.

Watch out: if you do not test the T&P valve at a home inspection you should explain why (risk of a building flood) and you should advise your client to have such a test performed by their plumber promptly on taking control of the property. Avoid an ugly surprise by explaining what could go wrong.

What if the TPR Valve Keeps Dripping

We may not know the cause but the most-common causes of drips at a TPR valve include:

Left-over water in the diverter tube

following a test (this will slow and then stop)
Excessive temperature or pressure:

A heating appliance that is at a too-high temperature or too-high pressure (a first check is to look at the temperature settings on the equipment and on a heating boiler to look at the system pressure: both should be below the valve-opening temperature and pressure given on the TPR valve label)
A defective or leaky relief valve

(try replacing the valve)
Water hammer or thermal expansion in the hot water or heating system can cause episodic or regular TPR valve leaks.
See complete details

and other causes of TPR valve leaks

at RELIEF VALVE LEAKS

Watch out: the reasons that a dripping or leaking relief valve is dangerous include failure to notice that the system the valve is intended to protect is already operating at an unsafe temperature or pressure, OR the risk that continued leakage leads to scale clogging of the valve so that it cannot open in an emergency.

T&P Valve Inspection Frequency

Virtually every temperature / pressure relief valve manufacturer whose product line includes TPR valves with a test lever or mechanism recommends that the temperature and pressure safety relief valve be tested, though the test interval recommended ranges from three years to six months, varying by type of inspection and valve type.

Typically a manufacturer recommends that the T&P valve should be inspected and tested annually and inspected by complete removal every three years.

Really? In nearly 50 years of building inspection and repair work I [DF] have never once found a residential water heater installation at which the T&P valve is inspected regularly much less annually.

Typically the valve is noticed and replaced when the building occupants or owner observe a leak. Nevertheless we urge readers, plumbers, and other building occupants and owners to be sure that the recommendations of their TPR or easing valve manufacturer are followed. Failing to do so is dangerous.

Details of TPR valve inspection, including other inspection points beyond the actual valve testing (discussed just below) are at RELIEF VALVES - TP VALVES - home

Annual T&P Valve Test

Following installation, the valve lever MUST be operated AT LEAST ONCE A YEAR to ensure that waterways are clear.

Certain naturally occurring mineral deposits may adhere to the valve, blocking waterways, rendering it inoperative. When the lever is operated, hot water will discharge if the waterways are clear. - Watts (2011)

Three-Year T&P Valve Inspection

Watch out: Temperature and pressure relief valves should be re inspected at least once every three years by a licensed plumbing contractor or authorized inspection agency to ensure that the product has not been affected by corrosive water condition and to ensure that the valve and discharge line have not been altered or tampered with illegally.

Certain naturally occurring conditions may corrode the valve or its components over time, rendering the valve inoperative. Such conditions are not detectable unless the valve and its components are physically removed and inspected.

An unauthorized person must not attempt to conduct this inspection.

Contact a plumbing contractor for a re inspection to assure continuing safety.

Failure to re inspect as directed could result in unsafe temperature or pressure build-up that can result in serious injury or death and/or severe property damage. - Watts (2011)

Should a Home Inspector Test a Temperature/Pressure Relief Valve?

The answer is: it's debatable.

Some inspectors test the valve, providing an extra level of expert safety inspection, while others, afraid of a flood or hoping to shorten their job-time by reducing their inspection scope, skip this step.

We have advice for inspectors in both camps.

OPINION: The T&P valve is a critical safety device on water heaters and heating boilers and is a standard safety device found in most buildings. In our opinion, omission of any inspection of the TPR valve whatsoever would be malpractice, putting building occupants at risk. A building professional should know better.

But what about going beyond visual inspection? Under most home inspection standards that expect the inspector to operate "normal homeowner or user controls" on building equipment, one could argue that the inspector both can and should "test" the TPR valve by lifting the test lever.

Watch out: The results of testing a T&P valve, if the valve won't close again, can be a flood of hot water in the building, risking burns, water damage, and considerable shouting.

Do not try to stop a leaky T&P valve by capping off the valve or its discharge tube.

You risk a fatal BLEVE EXPLOSION.

Speaking from personal experience, I [DF] have operated a T&P valve only to see the old valve spit out its valve seat washer, leading to a horrible hot water flood.

I was able to shut off the hot water and drain pressure quickly enough that there was not much mopping to be done, and happily the owner did not have precious antique carpeting or other vulnerable materials on the floor in the area of the water heater.

Watch out: the following is not a recommended procedure and would be unsafe:

Back in the day before I knew much about this hazard, during a plumbing job I made an emergency "Sunday night" replacement TPR valve seat washer (cut out of a piece of Tupperware©) to permit the owners to have hot water until the valve could be replaced the next day. Under normal circumstances this is not something you should attempt.

Hazards of an Obstructed or Blocked TPR Valve Test Mechanism

This photograph, courtesy of Kingston N.Y. building inspector Arlene Puentes, shows an unsafe temperature/pressure relief valve installation in an apartment building in Watertown, New York. Puentes reports that this condition was found in about ten water heaters.

Other water heater installation details were also found unsafe in these apartments, such as improper relief valve extenstion tubes and relief valve leaking.

The test lever on the TPR valve (silver handle pointed-to by our red arrow) would be used to manually open, test or flush the TP valve but at this installation it is blocked by having been placed up against a plaster wall.

[Click to en large any image]

Watch out: If the lift/test lever on a temperature/pressure relief valve is blocked from movement that prevents the valve from being tested - a step recommended at least annually by relief valve manufacturers.

Watch out: Depending on the relief valve model and design, a blocked relief valve test lever may prevent the valve from opening in response to pressure or temperature.

Really? Some building maintenance people or managers may fail to take this condition seriously, yet when this safety device is needed and cannot work, the water heater an explode, resulting in a catastrophic, sometimes fatal BLEVE explosion. OPINION: heaven forbid such a catastrophe should occur in this apartment complex, for which the building management is on-notice and responsible should such a disaster occur.

See BLEVE EXPLOSIONS for details.

Arlene Puentes [Website: www.octoberhome.com ] , an ASHI member and a licensed home inspector in Kingston, NY, holds five International Code Council Certifications, New York State DOS Certified Code Enforcement Official, ASHI Member 210232, NYS Home Inspector License No. 16000095212and has served on ASHI national committees (Bylaws, Standards), as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com She is a frequent technical contributor to InspectApedia.com.

Temperature/Pressure Relief Valve Engineering, Codes, Standards, & Instructions

American Water Heater Co., INSTALLATION INSTRUCTIONS FOR TEMPERATURE AND PRESSURE VALVE [PDF] - Retrieved 2018/04/21, original source: http://www.americanwaterheater.com/media/23796/6500260.pdf
ANSI: Relief Valves and Automatic Gas Shutoff Devices for Hot Water Supply Systems, ANSI Z21.22, and the Standard CAN1-4.4 Temperature, Pressure, Temperature and Pressure Relief Valves and Vacuum Relief Valves
ASME / ANSI PTC 25.3 Standards (USA)
ASME Pressure Steam Rating - the following warning is excerpted from Watts' TP-AND-ASME-SAFETY-RELIEF-VALVES [PDF] cited below.

Watch out: The ASME pressure steam rating should be considered with caution, because it represents the ability of the device to discharge steam pressure at the set pressure of the valve. For example, let’s consider a 150psi set relief valve with an ASME pressure steam rating of 1,437,600 BTU per hour.

Before this valve can deliver that rating, there must be generated within the tank over 150psi of steam pressure in order to actuate the valve.

This is certainly an unsafe condition for a non-ASME rated water heater tank. The tank could rupture and explode prior to reaching this ASME pressure rating. An ASME-rated tank is constructed to higher standards than a non-rated tank. It is important to understand which type of tank will be used in an application.

For all non-ASME-rated tanks, the CSA temperature steam rating should always be used.
Bradford White, ELECTRIC WATER HEATER INSTALLATION & OPERATING MANUAL [PDF] - Retrieved 2018/04/21, original source: http://www.bradfordwhite.com/sites/default/files/product_literature/238-44422-00P.pdf
Ball, J.F., PRESSURE RELIEF DEVICE INSPECTION REVIEW OF NBIC Part 2, par. 2.5 [PDF] (2016) - Retrieved 2018/04/21, original source: https://www.dir.ca.gov/dosh/pressure-vessels/documents/PRD-Inspection-NBIC.pdf Ball, J.F., P.E., Pressure Relief Device Inspection, NBIC 2 2.5 [PDF] (2016)
Ball, Joseph F., P.E., Field Repairs of Pressure Relief Valves Part 2: Testing Mr. Ball is the Director, Pressure Relief Department, National Board of Boiler and Pressure Vessel Inspectors, Technology of Steam, Bulletin of National Board of Boiler and Pressure Vessel Inspectors, (2014 pp 8-10) - Retrieved 2018/04/21, original source: https://www.nationalboard.org/SiteDocuments/Bulletins/SU2014.pdf

Mr. Ball is director of the National Board Pressure Relief Department. He is responsible for pressure relief device new construction and repair certification programs, and test lab operations. He is also responsible for the conduct of shop reviews of valve and rupture disk manufacturers, assemblers, repair organizations, and test laboratories, and is an ASME Authorized Observer for the National Board Testing Laboratory.

Mr. Ball is a professional engineer in the state of Ohio and is a National Board instructor for C and VR courses. He is a member of the ASME Section XI and the General Requirements Subgroup and Working group.

He is a member of the ASME Section XIII Committee on Overpressure Protection, and is the chair of the Section III Working Group on Pressure Relief and a member of the Subgroup on Component design. -http://www.nationalboard.org/NationaBoardNews.aspx?NewsPageID=1802
National Board contact: http://www.nationalboard.org/Index.aspx?pageID=102&ID=104

National Board of Boiler and Pressure Vessel Inspectors Mailing Address: 1055 Crupper Avenue Columbus, Ohio 43229-1183 USA, Phone: 614.888.8320 Email: information@nationalboard.org

Test Lab and Pressure Relief Operations, Mailing Address: 7437 Pingue Drive Worthington, Ohio 43085 Phone: 614.888.8320 PRD email: prd@nationalboard.org
Lab email: lab@nationalboard.org
California, City of Merced, RELIEF VALVE DISCHARGE PIPING PLUMBING CODE [PDF] based on UPC 608.5, building code interpretation regarding the discharge piping from water heater temperature-pressure relief valves based on the California Plumbing Code, Merced Civic Center 678 West 18th Street Merced, California 95340 Telephone: (209) 385-6834- Retrieved 2018/04/21, original source: https://www.cityofmerced.org/ civicax/filebank/blobdload.aspx?BlobID=19062
CROSBY PRESSURE RELIEF VALVE ENGINEERING HANDBOOK [PDF] Technical Document No. TP-V300, (1997), Crosby Valve, Inc., retrieved 2018/04/21, original source: http://www.isibang.ac.in/~library/onlinerz/resources/enghandbook3.pdf

Crosby USA Operations Executive and Sales Headquarters and Manufacturing Plant Crosby Valve Inc. 43 Kendrick Street P.O. Box 308 Wrentham, Massachusetts 02093-0308 Tel: (508) 384-3121

Crosby UK Operations Headquarters, Sales Office, and Manufacturing Plant Crosby Valve and Engineering Crosby Road Market Harborough Leics LE16 9EE, England Tel: (44) (1858) 467281
CROSBY RELIEF VALVE Series 800, 900 PRESSURE RELIEF VALVE INSTALLATION, MAINTENANCE, ADJUSTMENT INSTRUCTIONS [PDF] - Op. Cit. retrieved 2018/04/22, original source: http://50.244.15.10/techlib/Crosby/Crosby_ReliefValve_800_900_iom_D498.pdf
CROSBY PENTAIR 800-900 BLOWDOWN PRVs PRODUCT SPECIFICATIONS [PDF] retrieved 2018/04/22, original source: http://www.askalon.com/en/assets/document/Crosby-Pentair%20Omni%20800,%20900%20datasheet.pdf
CSA temperature steam rating for relief valves is used under ANSI Z 21.22.
European standard EN ISO 4126-1
Flowstar, SAFETY RELIEF VALVES [PDF] - Retrieved 2018/04/21, Flowstar (UK) Ltd., Units 1 & 2, Gillett Street Kingston-upon-Hull, HU3 4JA United Kingdom, Hull 01482 601030 hull@flowstar.co.uk Aberdeen 01224 392415 aberdeen@flowstar.co.uk Ireland 0353 76 8886057 ireland@flowstar.co.uk International +44 1482 601030 original source: https://www.flowstarvalveshop.com/pages/safety-relief-valves - see clip and pdf
Pentair Valves & Controls, PENTAIR PRV ENGINEERING HANBOOK [PDF] (2012) - Anderson Greenwood, Crosby and Varec Products, Pentair Valves & Controls, Retrieved 2018/04/21, original source: http://www.iomosaic.com/diersweb/docs/pvcmc-0296-us_tcm106-35825.pdf
Spirax Sarco, STEAM SYSTEM SAFETY VALVE INSTALLATION [PDF], Spirax Sarco Limited, Tel: K+44 (0) 1242 521361, Offices world wide, Website: http://www.spiraxsarco.com/ retrieved 2018/04/22, original source: http://www.spiraxsarco.com/Resources/Pages/Steam-Engineering-Tutorials/safety-valves/safety-valve-installation.aspx
Watts Corporation, TP-AND-ASME-SAFETY-RELIEF-VALVES [PDF] (2011), Watts USA: No. Andover, MA Tel: (978) 688-1811 Website: www.watts.com
Canada: Burlington, ON Tel: (905) 332-4090 Website: www.wattscanada.ca - Retrieved 2018/04/21, original source: https://www.questargas.com/ ForEmployees/ qgcOperationsTraining/Water Heaters/Misc_Temp and Pressure relief.pdf
Excerpt:

An exploding 30-gallon water heater has the force of about one pound of dynamite.and has the power to destroy a house and injure or kill those inside. Thankfully, explosions have been significantly reduced because temperature and pressure (T&P) relief valves are now being used nationally to protect water heaters from explosion.

T&P relief valves, when installed properly, prevent high water temperatures, which can cause flashing of hot steam at faucets or any water outlets in the system, or cause an explosion. And, they prevent high pressures, which can damage the water heater system piping or components.
Watts Water Technologies Co., WATTS LFN30 N30 INSTALLATION INSTRUCTIONS, RELIEF VALVES (DIAPHRAGM ACTUATED) [PDF] Retrieved 2018/04/21, original source: http://media.wattswater.com/1910203.f
Watch out: Excerpt:
These valves protect against excessive pressure only. To prevent excessive temperature above 212°F, which might result in a hot water explosion, combined temperature and pressure protection is essential. WATTS Combination Temperature and Pressure Relief Valves give this protection.
Watts, PRESSURE RELIEF VALVE 53L INSTALLATION MANUAL, Model 530C and LF530C Calibrated Pressure Relief Valve & Model 53, LF53, 111 and LF111 Pressure Relief Valves [PDF] Op. Cit., - Retrieved 2018/04/21, original source: http://www.watts.com/pages/_products_details.asp?pid=799
Excerpts:
Series 53L Pressure Relief Valves are used in residential applications to protect against excessive pressure on domestic storage tanks and tankless water heaters..... ANSI Z21.22 approved, design certified and listed by CSA, and UL listed.

Pressure Range: 75 to 175psi (5.2 to 12.1 bar), Standard Pressure Setting: 75psi (516.7 kPa), Optional Settings: 100, 125, and 150psi (6.9, 8.6, and 10.3 bar); Also available at 50psi (3.45 bar) setting.

...

Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: is it ok to snap the TPR valve shut or not?

2019/12/15 Anonymous asked by private email:

I recently tested the T&P valve on my electric water heater. I let it the snap back closed, as this is what a lot of websites said, and it appeared to test fine. However, I then found on your website, which said the lever is supposed to gently raised and lowered, or the valve could be damaged. I tested the valve again in this manner. Water flowed freely and it appears to have closed back properly.

(I didn't completely open the valve this time as the water heater's location can make this a messy affair.)

Is there anything else I need to do to make sure the valve is safe and wasn't damaged by letting it snap back?

Reply: details of temperature/pressure relief valve operation for testing: snap shut OK, avoid rough handling

Thank you for asking an important TPR valve test procedure safety question, Anon.

Indeed typical water heater manufacturer's instructions mention TPR valve testing procedures. Letting the valve "snap back" closed helps assure that the stop valve seats securely against the washer. I've done exactly that when the valve was dripping after a test.
Here is a typical manufacturer's instruction

To actuate the valve, hold the trip lever fully open for approximately five seconds in order to flush the valve seat free of any sediment. Then permit the valve check to snap shut. - source: American Water Heater Co., - Source: AMERICAN WATER HEATER INSTALLATION INSTRUCTIONS FOR TEMPERATURE AND PRESSURE VALVE [PDF] -

However in this article we noted that Rheem has pointed out [citation needed] that rough handling of the relief valve test lever, such as allowing it to "snap" closed, can damage the temperature and pressure relief valve - a dangerous condition that could lead to a water heater explosion or BLEVE EXPLOSION.

Some Rheem water heater manuals and instructions are not-specific on this point, such as

At least once a year, lift and release the lever handle on the temperature pressure relief valve, located near the top of the water heater, to make certain the valve operates freely. Allow several gallons to flush through the discharge line to an open drain. - Source: RHEEM ELECTRIC WATER HEATER MANUAL [PDF]

It was Rheem's warning that prompted me to warn readers about overly-aggressive "snapping shut" or torturing TPR valves.

My opinion is that normal operation of the TPR valve, including simply letting it close on its own, ought to be fine. I don't think that the snap-back is going to damage a valve that's otherwise in good condition. But an old TPR valve that has not been tested in sometime may have a dried-out washer that will fail when the valve is tested. In that case the valve needed to be replaced even before

On rare occasions with an old valve whose valve seat was scale-coated and in another instance when the valve internal washer was dried-out, snapping back the valve led to an obvious failure: the valve dripped constantly.

...

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