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How to fix a boiler pressure leak

We'll check the pressure gauge, rule out expansion tank or fill valve issues, replace the relief valve if worn, and tell you when to call a plumber.

Troubleshooting · Home plumbing
20–45 min
What you'll need
  • Wrench set
  • Replacement pressure relief valve (if needed—match the rating on the old valve)
  • Thread sealant (Teflon tape or pipe dope)
Step 1 of 7

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Steps

Goal: Confirm the leak is from the pressure relief valve, check the pressure gauge, and fix or escalate.

  • Shut off the boiler and let it cool for at least an hour.
  • Good: Boiler is off and cool. Proceed to Check where the water is coming from.
  • Bad: Boiler is still hot—wait longer before touching.

Locate the leak

Goal: Confirm the leak is from the pressure relief valve and not from fittings or the tank.

  • Dry the area around the boiler. Turn the boiler on briefly and watch where water appears.
  • Good: Water drips from the relief valve or its discharge pipe—pressure-related. Proceed to Check the pressure gauge.
  • Bad: Water from fittings or tank seam—see How to fix a boiler leak.

Check the pressure gauge

Goal: Determine if pressure is high (expansion tank or fill valve) or normal (relief valve worn).

  • Look at the pressure gauge. Normal is 12–15 psi for most residential boilers.
  • Good: Pressure is in the normal range. Proceed to Replace relief valve path.
  • Bad: Pressure is above 15–20 psi. See When to get help.

Replace relief valve

Goal: Replace a dripping pressure relief valve that will not seal when pressure is normal.

  • Buy a replacement that matches the pressure rating on the old valve (often 30 psi). Shut off the boiler and relieve pressure.
  • Unscrew the old valve with a wrench. Install the new one with thread sealant. Tighten firmly but do not over-tighten.
  • Turn the boiler back on. Confirm no drips from the valve or discharge pipe.
  • Good: No drips when the boiler runs. Proceed to Verification.
  • Bad: Still drips or pressure rises—call a plumber.

When to get help

Call a plumber if:

  • The pressure gauge reads high (above 15–20 psi)—expansion tank or fill valve likely failed.
  • The expansion tank sounds full or dull when you tap it (waterlogged).
  • The tank itself is leaking.
  • You are not comfortable working on heating equipment.

If you smell gas, evacuate immediately. Do not turn on lights or appliances. Call 911 or your gas utility from outside.

Verification

  • The pressure gauge stays in the normal range (12–15 psi) when the boiler runs.
  • No water drips from the pressure relief valve or its discharge pipe.
  • The floor around the boiler stays dry after 15–20 minutes of operation.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify water drips from the pressure relief valve or its discharge pipe.
  2. Check pressure gauge Confirm pressure is 12–15 psi (normal) or high (above 15–20 psi).
  3. High pressure Call a plumber—expansion tank or fill valve likely failed.
  4. Normal pressure—replace relief valve Replace the relief valve if it drips and will not seal.
  5. Call a plumber Tank leaking, expansion tank waterlogged, or not comfortable—call a professional.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Pressure gauge reading (psi)
  • Whether the relief valve drips constantly or only when tested
  • Whether the expansion tank sounds hollow or waterlogged when tapped
  • Steps already tried

Is water dripping from the pressure relief valve or its discharge pipe?

Dry the area and run the boiler briefly. Watch where water appears.

Dry the area around the boiler. Turn the boiler on briefly and watch where water appears. Good: water drips from the pressure relief valve or its discharge pipe—pressure-related leak. Bad: water from fittings or tank seam—see How to fix a boiler leak.

Yes No

You can change your answer later.

Different leak—see boiler leak guide

Water is from fittings or tank. See How to fix a boiler leak for general boiler leaks.

Done

Does the pressure gauge read above 15–20 psi?

Normal is 12–15 psi. High pressure means expansion tank or fill valve issue.

Check the pressure gauge on the boiler. Normal is 12–15 psi. High (above 15–20 psi): expansion tank or fill valve failed—call a plumber. Normal: relief valve may be worn—test and replace if needed.

Yes No

You can change your answer later.

Call a plumber—high pressure

High pressure means the expansion tank or fill valve has failed. Do not attempt to fix yourself. Shut off the boiler and call a plumber.

Done

Does the relief valve stop dripping when you release the lever?

Lift the lever briefly. Water should flow, then stop when released.

Lift the pressure relief valve lever briefly. Water should discharge, then stop when you release. Stops: valve may have been stuck—monitor. Keeps dripping: valve is worn—replace it.

Yes No

You can change your answer later.

Monitor the valve

The valve stopped dripping when you released the lever. It may have been stuck temporarily. Run the boiler and monitor—if it drips again, replace the valve.

Done

Replace the relief valve

Replace the pressure relief valve with one that matches the pressure rating. Shut off the boiler, relieve pressure, unscrew the old valve, install the new one with thread sealant. Confirm it seals when the boiler runs.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why does my boiler pressure relief valve leak?
Common causes: a worn or stuck relief valve that will not seal; high pressure from a failed expansion tank; or a stuck fill valve adding too much water. Check the pressure gauge first—if it reads high, the expansion tank or fill valve is the cause.
Can I fix a boiler pressure leak myself?
Yes, if the pressure gauge reads normal and the relief valve drips—you can replace the valve. If the pressure is high, the expansion tank or fill valve is likely the cause; call a plumber. Do not attempt to repair a leaking tank.
When should I call a plumber for a boiler pressure leak?
Call a plumber if the pressure gauge reads high (above 15–20 psi), the expansion tank is waterlogged or failed, the tank itself is leaking, or you are not comfortable working on heating equipment. High pressure can be dangerous.

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