What a T&P Valve Is and How to Fix It

A T&P valve, also known as a temperature and pressure relief valve, is an important safety component found on many types of tanks that heat or store liquids under pressure. The T&P valve serves a crucial purpose – to prevent explosion or rupture of the tank due to excessive pressure buildup.

In this comprehensive guide, we’ll cover everything you need to know about T&P valves, including:

What Is a T&P Valve and Why Is It Important?

A T&P valve, short for temperature and pressure relief valve, is a safety device installed on pressurized tanks and heaters like water heaters, boilers, and steam radiators. It serves as a fail-safe mechanism that automatically opens to release excess pressure from inside the tank if the temperature or pressure rises to dangerous levels.

The T&P valve protects the tank from damage or explosion due to excess pressure buildup caused by:

  • Excessive heating of the water inside the tank
  • Malfunctioning thermostats failing to shut off the heating elements
  • Clogged pipes preventing pressure from escaping

The valve is usually installed on the side of the tank. It remains closed under normal working conditions. If the pressure exceeds the valve’s pre-set limit, the valve will automatically open to release the excess pressure. This lowers the pressure inside the tank and prevents an explosion.

Some key reasons why a properly functioning T&P valve is critical:

  • Prevents explosions – Excessive pressure can make a hot water tank explode, endangering lives and property. The T&P valve safely vents out the extra pressure.
  • Averts tank ruptures – High pressure could damage or rupture a tank. The T&P release prevents this by keeping pressure below dangerous levels.
  • Reduces risk of scalding – Water heated above 125°F can cause severe scalds. The T&P valve limits temperature to a safe level.
  • Saves repair costs – A blown out hot water tank is expensive to replace. The T&P valve minimizes blowouts.
  • Prolongs system lifespan – Excess pressure wears out plumbing systems quicker. The T&P valve reduces pressure for longer equipment life.
  • Meets safety codes – Building codes require T&P valves on high-temperature, pressure systems for safety.

In short, the humble T&P valve plays an indispensable role in preventing disastrous tank failures and ensuring safe, efficient operation of pressurized heating systems.

How Does a T&P Valve Work?

A T&P valve is an automatic release valve designed to open if predetermined temperature or pressure limits are exceeded. Here is a simple overview of how it works:

  • The valve has a sensing element that reacts to temperature and pressure changes inside the tank. Common sensor types are bellows, bourdon tubes, and expanding rods.
  • The sensor connects to a spring-loaded disc or lever. Under normal conditions, the sensing element keeps the disc/lever pressed tightly shut against an orifice opening.
  • When the temperature or pressure in the tank gets too high, the sensor expands or flexes enough to overcome the spring force. This lifts the disc/lever off the orifice.
  • With the orifice uncovered, the excess pressure and hot water or steam escapes through the T&P valve to the drainage pipe.
  • As the pressure is released, the sensor contracts and the spring pushes the disc/lever back down, closing off the orifice again. This stops the flow.
  • The valve keeps automatically modulating open and shut as needed to vent excess pressure, until conditions in the tank return to normal working limits.
  • The valve re-closes only when both pressure and temperature are reduced below the valve’s pre-set relief limits.

The valve discharge pipe directs the hot water/steam release to a safe drainage location, preventing injury or property damage.

T&P Valve Pressure Settings

T&P valves are preset to open at a specific pressure limit by the manufacturer. The pressure relief setting is stamped on the valve and depends on the tank type:

  • Storage tank T&P valves are set to open at 150 psi
  • Hot water heaters have T&P valves set to 150 psi or 125 psi
  • Low pressure boilers have T&P valves set to 15 psi
  • High pressure steam boilers have settings up to 250 psi

Always check your system’s valve for its pressure relief setting. Install a replacement T&P valve with the same pressure rating as the original. If the limit is too high, the valve won’t open soon enough to prevent damage. And if it’s too low, the valve will leak unnecessarily.

T&P Valve Temperature Settings

The temperature relief setting is also marked on the T&P valve and varies based on the system:

  • On water heaters, the common T&P valve temperature setting is 210°F
  • For space heating steam boilers, the limit is 250°F
  • Low temperature hot water boilers have T&P valves set to 220-240°F
  • Pool heaters and similar low pressure systems use 150°F valves

Match the new T&P valve’s temperature rating if replacing an old one. The setting helps prevent dangerous overheating but shouldn’t be so low that the valve leaks prematurely.

Signs of a Faulty T&P Valve

A faulty T&P valve can completely fail to release excess pressure. Or it may leak constantly, losing efficiency and wasting energy. Here are signs of T&P valve problems:

  • Blocked outlet – Debris clogs the valve outlet, preventing pressure release. This is extremely dangerous.
  • Continuous dripping/leaking – If the valve leaks non-stop, the release limits are too low or something is sticking.
  • No dripping when manually activated – If no water comes out when you test the lever, the valve is blocked.
  • Chattering sound – Rapid opening and closing during heating cycles indicates improper pressure settings.
  • Rust/corrosion – Release capacity is reduced, causing failure risk.
  • Bulged/damaged/leaking tank – The valve may have failed to release excess pressure.
  • Age over 10 years – Older valves become mineral blocked, rigid or inaccurate.
  • No manufacturer stamp – Lack of code stamping means it’s likely an obsolete valve in need of replacement.

Any of these signs point to the need to test, repair or replace the T&P valve before a serious system failure occurs.

How to Test a T&P Valve

It’s recommended to test the T&P valve at least annually to ensure it is functioning properly before a dangerous pressure event arises. Follow these steps:

1. Wear eye protection. Releasing hot water or steam can be hazardous.

2. Locate the valve test lever or button. It is typically on the top, side or end of the valve.

3. Place a container under the valve outlet. This will catch the released liquid.

4. Briefly activate the test lever/button. This should vent a rush of hot water for a few seconds.

5. Check flow consistency. Release should have strong, steady flow without obstructions.

6. Let the valve re-close completely. Confirm it stops the water/steam flow and re-seals drip-free after releasing.

7. Drain all released water safely. The water may be extremely hot and under pressure.

8. Refill the tank if needed. Run a heating cycle to get back up to temperature.

9. Repeat test 2-3 times per year. Schedule a biannual testing routine.

If at any point the valve fails to open, drips continuously, or the flow is blocked or weak, it’s time for T&P valve repair or replacement.

How to Maintain and Clean a T&P Valve

Routine T&P valve maintenance helps extend its working life and ensure reliable pressure release in emergencies:

  • Remove debris – Use a stiff wire brush to clear any dirt, scale or debris blocking the valve seat and outlet.
  • Descale regularly – Soak in a descaling solution or vinegar for an hour to dissolve lime deposits.
  • Confirm drainage – When activated, the valve should gush fully until closed. Poor drainage indicates blockage.
  • Listen for chatter or leaks – Any noise from the valve in normal operation means a problem is developing.
  • Check relief settings – Settings can drift over time. Compare pressure/temp settings to tank ratings.
  • Replace old valves – Any valve 10+ years old should be replaced as a preventive measure.
  • Keep outlet piping clear – Ensure discharge pipe is properly sloped to fully drain water away after valve closes.
  • Have pros assess annually – Plumbing and HVAC technicians can detect issues during annual tune-ups.

Proper maintenance helps keep the T&P valve in prime working order for releasing damaging pressure buildup before the tank or heating system sustains damage.

How to Replace a Faulty T&P Valve

If testing reveals the T&P valve is no longer working properly, replacement of the entire valve is required. Here is an overview of the replacement process:

Step 1: Shut off water and power supply

Start by switching off power to the water heating system, as well as shutting off the cold water intake valve. This is crucial to prevent getting scalded and reduces water leakage.

Step 2: Drain the tank

Open the tank drain valve to fully drain the tank. This eliminates pressure so the old T&P valve can be safely removed.

Step 3: Remove old T&P valve

Unscrew the old T&P valve from the tank. Use pipe wrenches if needed to unscrew the threaded connection.

Step 4: Clean valve seat and outlet

Use a wire brush and descaling solution to thoroughly clean mineral deposits from the valve threads, seat, and discharge pipe. Debris can prevent a tight seal.

Step 5: Install new T&P valve

Wrap the threads with Teflon tape. Hand tighten the new valve first, then finish tightening with wrenches to avoid over-torquing.

Step 6: Reconnect plumbing and refill tank

Reconnect water lines, refill the tank, and turn the power back on. Bleed radiators if needed to remove trapped air.

Step 7: Test the new T&P valve

Follow the test procedure outlined earlier. Confirm strong flow and a complete sealing shutoff when the test lever is released.

With a properly installed replacement, your tank and plumbing system now have full protection against dangerous pressure buildup once again.

Troubleshooting Common T&P Valve Problems

Here are some common T&P valve troubleshooting scenarios and remedies:

Problem: T&P valve leaks water constantly

Solution: The pressure or temperature relief setting is too low. Replace with a valve with higher pressure/temp limits. A water softener may be needed if the leak is due to mineral deposits.

Problem: No water released when T&P lever is tested

Solution: Discharge pipe is clogged. Clear debris from the outlet pipe and re-test. The valve may need replacement if flow isn’t restored.

Problem: Weak water flow when testing T&P valve

Solution: Partial blockage due to buildup or debris. Clean outlet and valve seat areas thoroughly to remove obstructions.

Problem: Chattering or hammering noise from T&P valve

Solution: Water pressure is too high. Adjust your pressure reducer to lower water system pressure below the T&P valve’s limit.

Problem: Tank leakage from area where T&P valve connects

Solution: Seal is compromised due to overtightening, gasket failure or corrosion. Replace the T&P valve and carefully tighten to proper torque.

Addressing T&P valve problems promptly prevents pressure emergencies that can lead to dangerous tank failures, floods or water damage. Call a professional plumber or HVAC technician for any repairs needed beyond basic maintenance.

Frequently Asked Questions

What is the cost to replace a T&P valve?

A new T&P valve costs $20 to $50 on average for a residential unit. However, with labor for installation, the total T&P valve replacement cost is typically $200 to $250.

Where does the T&P valve discharge pipe need to point?

The T&P valve discharge pipe should point down towards the floor and exit around 6 inches above a drain. This safely directs hot water release to waste.

How do I stop my T&P valve from leaking?

A constantly leaking T&P valve needs replacement. The release limits are too low or sediment is preventing full closure. Installing a new, properly rated T&P valve will solve leakage.

Is it OK to plug a leaking T&P valve?

Never plug or cap a leaking T&P valve. This prevents pressure release and can lead to an explosion risk. Always replace a leaking T&P valve immediately.

Can I replace just the gasket on my T&P valve?

The gasket cannot be replaced separately – the entire T&P valve assembly must be replaced to ensure proper pressure relief capability.

My T&P valve is old but not leaking. Do I need to replace it?

T&P valves older than 10 years should be replaced proactively even if not visibly leaking yet. Components degrade over time, putting safety at risk.


The humble T&P valve plays a vital and often overlooked role in preventing disastrous water heater explosions and other heating system failures. While designed to operate automatically in emergencies, T&P valves do require periodic testing and maintenance to keep them in good working order. Replacing old and malfunctioning valves before problems arise is key to continued safe operation.

With a properly sized and adjusted T&P valve, plus regular inspection and cleaning, your hot water tanks, boilers, and other pressureized heating equipment will remain protected for years to come. Be sure to consult qualified plumbing professionals if you have any concerns about an aging or problematic T&P valve requiring replacement. Proper installation and pressure limits are crucial for safety. With the right valve in place, you can rest easy knowing potential pressure hazards will be automatically mitigated.