If your water heater pressure relief valve keeps opening, you’re not alone. This is one of the most common (and frustrating) water heater issues homeowners face—and it usually points to a real pressure or temperature problem that can’t be ignored.
This guide explains why your T&P valve keeps opening, how to diagnose the cause, and the smartest long-term fixes.
Quick Answer: Why Does Your Pressure Relief Valve Keep Opening?
The three most common reasons are:
Excessive water pressure (above 80 PSI in the home)
Thermal expansion (especially if you don’t have an expansion tank)
A faulty or worn-out relief valve
Each one can force the T&P valve to release water to prevent tank explosion.
Why the Pressure Relief Valve Keeps Opening (How It Works)
Your water heater’s T&P valve (Temperature & Pressure Relief Valve) is a safety device designed to release water if:
Temperature exceeds ~210°F (99°C)
Pressure exceeds 150 PSI
If pressure or temperature rises above these limits, the valve opens automatically to prevent catastrophic tank failure.
So if it keeps opening (or leaking slowly), it means the system is repeatedly reaching unsafe pressure or temperature levels—or the valve itself is damaged.
5 Reasons Your Water Heater Pressure Relief Valve Keeps Opening
1. Water Pressure Is Too High (Above 80 PSI)
High incoming water pressure is the #1 cause of recurring T&P valve discharge.
Symptoms of high pressure
Relief valve opening randomly, especially at night
Toilet fill valves hissing
Popping or banging pipes (water hammer)
How to check water pressure
Use a garden-hose pressure gauge on an outdoor spigot. Normal pressure = 40–60 PSI.
If it’s over 80 PSI, the T&P valve will open.
Solution
Install or replace a pressure reducing valve (PRV) on the main line.
2. Thermal Expansion (No Expansion Tank Installed)
When water heats up, it expands. In a closed plumbing system, that expansion has nowhere to go—so pressure rises until the T&P valve opens.
This is extremely common in homes with:
New water heaters
Backflow preventers
Check valves
Pressure reducing valves
Why new heaters make this worse
New tanks heat water more efficiently ⇒ more pressure increase.
Solution
Install a thermal expansion tank on the cold water inlet.
This permanently solves most “new water heater relief valve keeps opening” issues.
3. Valve Pressure Rating Too Low
A standard T&P valve is rated for 150 PSI. Cheaper or mismatched valves may open early.
How to check
Look at the valve’s tag:
Pressure rating
Temperature rating
ANSI/CSA compliance
If it’s below 150 PSI, it may open unnecessarily.
Solution
Replace with a quality, correctly rated valve.
4. Thermostat Malfunction (Water Too Hot)
If the thermostat is faulty or set too high, the water can exceed safe temperatures, causing the relief valve to open.
Signs the water is too hot
Steam from faucets
Scalding temperatures
Popping noises inside the tank
How to check
Set the thermostat to 120°F
If overheating continues → thermostat is malfunctioning
Solution
Replace the thermostat or heating element (in electric heaters).
5. Defective or Worn-Out Relief Valve
Relief valves wear out over time—corrosion, mineral deposits, and age can all cause improper sealing.
How to test the valve
Lift the test lever briefly.
Ensure water flows freely.
Release the lever.
Valve should reseal completely.
If it keeps dripping or opening → replace it.
A high-quality valve prevents nuisance opening and lasts longer.
How to Diagnose the Problem (Step-by-Step)
Check home water pressure (should be under 80 PSI)
Inspect for a thermal expansion tank
Verify the T&P valve’s pressure rating
Monitor water temperature stability
Inspect valve for corrosion, mineral buildup, or leaks
Check if the relief valve opens only after heating cycles
Test the valve manually (as above)
This process will pinpoint the root cause 95% of the time.
Permanent Solutions to Stop the Relief Valve from Opening
✔ Install a Pressure Reducing Valve (PRV)
Controls main line pressure → reduces stress on the system.
✔ Add a Thermal Expansion Tank
Absorbs expanded water volume → prevents pressure spikes.
✔ Replace Faulty or Underrated T&P Valve
Ensures accurate pressure protection.
✔ Adjust or Replace Thermostat
Prevents overheating.
When these solutions are combined, the problem is permanently resolved.
Cost Analysis
| Item | DIY Cost | Professional Cost |
|---|---|---|
| Pressure gauge | $10–$20 | – |
| Replace T&P valve | $15–$35 | $120–$200 |
| Install expansion tank | $40–$80 | $250–$450 |
| Install PRV | $60–$120 | $300–$600 |
| Thermostat replacement | $20–$40 | $150–$300 |
Most cost-effective fix:
Expansion tank + PRV
This combination solves 80%+ of recurring T&P valve issues.
