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How to fix a radiator leak

We'll locate the leak, tighten or replace the valve packing, and tell you when to call a plumber.

How-to · Home plumbing
15–30 min
What you'll need
  • Wrench set
  • Valve packing (graphite or PTFE)
  • Replacement valve (if needed)

At a glance

  • Shut off the radiator valve and let it cool before working.
  • Locate the leak—valve stem, valve body, or radiator seam.
  • Tighten the packing nut to stop leaks at the valve stem.
  • Replace the valve packing or the valve if tightening does not work.
  • Call a plumber if the radiator body is leaking or you cannot stop the leak.
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Steps

Goal: Shut off the valve, locate the leak, fix the valve packing or valve, and know when to call a plumber.

  • Shut off the radiator valve and let it cool.
  • Good: Valve is closed and radiator is cool. Proceed to Locate the leak.
  • Bad: Valve will not close—call a plumber.

Locate the leak

Goal: Identify where the water is escaping.

  • Dry the valve and radiator. Turn the valve on briefly and watch where water appears—at the valve stem, valve body, or radiator.
  • Good: You see water emerge from one or more spots. Proceed to Tighten packing nut or Replace valve based on location.
  • Bad: Cannot locate—call a plumber.

Tighten packing nut

Goal: Stop leaks at the valve stem.

  • Shut off the valve. Tighten the packing nut a quarter turn. Turn the valve on and check.
  • Good: No drip at the stem.
  • Bad: Still leaks—replace the packing or the valve.

Replace valve

Goal: Fix a cracked valve or one that will not seal.

  • Shut off the supply and drain the radiator. Remove the old valve and install a matching replacement.
  • Good: No leak when the system runs.
  • Bad: Radiator body is leaking—call a plumber.

When to get help

Call a plumber if:

  • The radiator body itself is leaking.
  • The valve will not shut off.
  • Tightening and packing replacement do not stop the leak.

Do not force stuck valves—you can cause a larger leak.

Verification

  • No drips at the valve stem, valve body, or radiator when the system runs.
  • Valve opens and closes smoothly.
  • Radiator heats normally.

Reviewed by Blackbox Atlas

Frequently asked questions

Why does my radiator leak?
Common causes: worn valve packing at the stem, a loose packing nut, a cracked valve, or corrosion at the radiator. Valve leaks are often fixable; body leaks usually need a plumber.
Can I fix a radiator leak myself?
Yes, for leaks at the valve stem or valve body. Shut off the valve first. If the radiator body is leaking, call a plumber—radiators can be under pressure.
When should I call a plumber for a radiator leak?
Call a plumber if the radiator body is leaking, the valve will not shut off, or tightening and packing replacement do not stop the leak. Do not force stuck valves.

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