How to fix a boiler leak
We'll locate the leak, tighten fittings or replace the pressure relief valve, and tell you when to call a plumber.
What you'll need
- Wrench set
- Replacement pressure relief valve (if needed)
- Thread sealant (Teflon tape or pipe dope)
At a glance
- Shut off the boiler and let it cool before working on it.
- Locate the leak—fittings, pressure relief valve, or tank seam.
- Tighten loose fittings with a wrench; do not over-tighten.
- Replace a dripping pressure relief valve if it will not seal.
- Call a plumber if the tank is leaking, pressure is high, or you are unsure.
Quick triage — pick your path
Get started
Choose the option that matches what you see. You can jump straight to that section.
- Follow this guide Work through the full procedure from shutting off the boiler to fixing the leak.
- Locate the leak You want to identify where the water is coming from first.
- Tighten fittings The leak is at a pipe or valve connection.
- Replace pressure relief valve The pressure relief valve drips and will not seal.
- When to call a plumber The tank is leaking, pressure is high, or you are not comfortable.
Steps
Goal: Shut off the boiler, locate the leak, fix fittings or the pressure relief valve, and know when to call a plumber.
- Shut off the boiler and let it cool for at least an hour.
- Good: Boiler is off and cool. Proceed to Locate the leak.
- Bad: Boiler is still hot—wait longer before touching.
Locate the leak
Goal: Identify where the water is escaping.
- Dry the area around the boiler. Turn the boiler on briefly and watch where water appears—at fittings, the pressure relief valve, or the tank.
- Good: You see water emerge from one or more spots. Proceed to Tighten fittings or Replace pressure relief valve based on location.
- Bad: Cannot locate—call a plumber.
Tighten fittings
Goal: Stop leaks at pipe or valve connections.
- Shut off the boiler. Use a wrench to snug loose fittings—do not over-tighten. Turn the boiler back on and check for leaks.
- Good: No drips at the fittings.
- Bad: Still leaks or the tank is leaking—call a plumber.
Replace pressure relief valve
Goal: Fix a dripping pressure relief valve that will not seal.
- Buy a replacement that matches the pressure rating. Shut off the boiler and relieve pressure. Unscrew the old valve and install the new one with thread sealant.
- Good: No drips when the boiler runs.
- Bad: Still drips or pressure is high—call a plumber.
When to get help
Call a plumber if:
- The tank itself is leaking.
- The pressure gauge reads high (above normal range).
- The leak is at a welded seam.
- You are not comfortable working on heating equipment.
Do not attempt to repair a leaking tank—it needs replacement.
Verification
- No drips at fittings, the pressure relief valve, or the tank when the boiler runs.
- Pressure gauge reads in the normal range.
- Boiler heats normally.
Reviewed by Blackbox Atlas
Frequently asked questions
- Why does my boiler leak?
- Common causes: loose fittings at pipes or valves, a faulty pressure relief valve that drips, or corrosion at the tank. A leaking tank often means the boiler needs replacement.
- Can I fix a boiler leak myself?
- Yes, for minor leaks at fittings or a dripping pressure relief valve. Shut off the boiler first. If the tank itself is leaking or pressure is high, call a plumber.
- When should I call a plumber for a boiler leak?
- Call a plumber if the tank is leaking, the pressure gauge reads high, the leak is at a welded seam, or you are not comfortable working on heating equipment. Boilers operate under pressure—safety first.
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