How to Troubleshoot a Hot Water Heater Pressure Relief Valve That Keeps Opening
A continuously leaking or popping open hot water heater pressure relief valve can be a nuisance and waste energy. Identifying the root causes and properly repairing the issue provides long-term relief for your home's plumbing system.
This vital safety component protects against dangerous pressure buildups and overheating. When operating normally, the valve should only open occasionally to release excess pressure. Frequent or constant valve opening indicates a problem needing your attention.
What Is a Hot Water Heater Pressure Relief Valve?
A pressure relief valve, also called a T&P (temperature and pressure) valve, is a safety device installed on residential water heaters. It serves two key functions:
- Limits tank pressure to a safe level, usually 150 psi.
- Allows hot water and steam to escape if temperature exceeds 210degF.
By automatically releasing excess heat and pressure, the valve prevents catastrophic tank explosions. It's required by building codes on all water heaters as a critical fail-safe.
How a T&P Valve Works
A T&P valve is normally closed. Inside is a spring that keeps the valve sealed until pressure or temperature get too high. If either reading exceeds the valve's preset safety limits, the spring compresses. This allows the valve to pop open and release the overheated water or excess pressure.
The valve should close again once pressure and temperature drop to safe levels. Constant leaking or dripping typically means the valve is broken or not seating properly.
Why Does the Pressure Relief Valve Keep Opening?
Frequent popping open or leaking from the pressure relief valve usually indicates an underlying problem with the water heater. Here are some of the most common causes:
- Faulty thermostat - A stuck thermostat can allow the tank to overheat, triggering the valve.
- Sediment buildup - Mineral deposits and scale may prevent the valve from sealing fully.
- Increased water pressure - Spikes in home water pressure overcome the valve spring.
- Damaged/defective valve - Imperfections in the valve mechanism can prevent it from closing.
- No thermal expansion tank - Excess pressure has nowhere to go and forces open the valve.
Signs of Excess Pressure and Temperature
How can you tell it's increased internal pressure or temperature making the valve open repeatedly?
With excess pressure, the valve will typically pop open with a hissing sound and release a burst of water. This sudden pressure drop may cause the water to sputter or run cold temporarily.
High temperature causes steam or boiling water to discharge steadily. This flows out until the tank cools down. You may hear bubbling or churning sounds from the escaping hot water.
Troubleshooting a Leaky Pressure Relief Valve
Always exercise caution when inspecting a hot water heater pressure relief valve. The discharging water may be scalding hot. Ensure the power or fuel supply is off before beginning.
Follow these troubleshooting steps to diagnose the issue:
- Visually inspect the valve and discharge pipe for damage, blockages, or leaks.
- Check the tank temperature settings and thermostat operation.
- Test and monitor water system pressure to identify spikes.
- Drain and flush the tank to remove mineral deposits.
- Replace the relief valve or thermostat if faulty.
Inspecting the Valve and Discharge Pipe
First, check the physical valve for cracks, corrosion, stuck mechanisms, or improper fittings. The discharge pipe should be angled downwards and free of kinks. Blockages prevent relief of pressure or steam.
A small weep of water may indicate a fouled valve seat. Try lifting the lever briefly to flush sediment. Replace the valve if worn out or damaged.
Checking Temperature and Thermostat
Use a thermometer to check the tank's water temperature. If constantly higher than the 120degF standard, the thermostat likely needs adjusting. A stuck thermostat that fails to cut off the heat is a common problem.
Test thermostat operation by lowering the setting 10 degrees. Monitor tank and outlet water temperature for a response. Replace faulty thermostats immediately.
Repairing a Pressure Relief Valve That Leaks Continuously
If the valve drips constantly even after troubleshooting, repairs are needed to stop the wasteful water loss and prevent damage.
Tightening the Valve Connection
Loose valve fittings allow water to leak through under pressure. Carefully tighten the threaded connection to the tank. Do not overtighten or you may damage the valve seat.
Clearing Debris from the Valve Seat
Sediment, minerals, and other debris trapped under the valve seat prevent it from sealing completely. Gently scrape and flush the seat clear using a toothbrush or water jet.
Replacing a Worn or Damaged Relief Valve
For valves that are corroded, mechanically stuck, or otherwise defective, replacement is the permanent solution. Use a compatible new relief valve rated for your water heater's specs.
Remove the old valve and install the replacement using pipe tape on the threaded fittings. Test to confirm the leak has stopped.
Preventing Continuous Pressure Relief Valve Leaks
To stop repeat valve opening or leaks, address the root causes:
- Install a thermal expansion tank
- Lower the thermostat temperature setting
- Use a water pressure regulator
- Drain and flush the tank regularly
- Have an annual heater maintenance check
Using a Thermal Expansion Tank
Adding an expansion tank on the water supply line gives excess pressure a place to go. This prevents pressure spikes from forcing open the relief valve.
Make sure to size the tank appropriately and check the precharge pressure yearly.
Lowering the Temperature Setting
Thermostats set too high cause repeated valve openings due to excessive heat. Lower to 120degF if currently set higher. Also check the accuracy with a thermometer.
When to Call a Professional for Assistance
For DIY-averse homeowners or complex plumbing issues, seek professional assistance for a leaky pressure relief valve.
Call a water heater specialist if you encounter:
- Leaks you cannot stop after troubleshooting
- Defective valves requiring replacement
- Inaccessible valve locations
- Water pressure problems
- Rust and corrosion damage
- Safety or building code concerns
A licensed plumber or HVAC technician has the skills, experience, and tools to fully diagnose issues and make all necessary repairs for safe operation.
Replacing a Faulty Pressure Relief Valve
When a pressure relief valve is too damaged or mineral-fouled to seal properly, replacing it is the fix. This straightforward repair restores protection against excessive pressure and temperature.
Choosing the Correct Replacement Relief Valve
Bring the old valve to the hardware store to match capacity, dimensions, and connections. The new valve must have the same pressure (psi) and temperature (degF) ratings as the original model.
Proper Installation Guidelines
Follow manufacturer instructions to install the new valve correctly. Use pipe tape on the threads. Position the discharge pipe to point downward to drain safely.
Briefly lift the lever to flush the valve after installation. Check for leaks over the first few days to confirm normal operation.