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Plumbing Leaks

Why Is My Water Heater Leaking?

A leaking water heater needs quick attention — some causes are simple fixes, others mean the tank is done.

Act Now

Can cause significant damage quickly. Identify the source within 24 hours.

The Short Answer

T&P Relief Valve Discharge. A leaking water heater needs quick attention — some causes are simple fixes, others mean the tank is done.

Most Likely Causes (Ranked)

1

T&P Relief Valve Discharge

Very Common

The T&P valve opens at 210°F or 150 PSI. Frequent discharge = high pressure, thermostat above 120°F, or no expansion tank.

How to tell: Water from brass valve on side or discharge pipe to floor. Water is hot.
2

Drain Valve Leak

Common

Bottom drain valve has loose connection, worn washer, or corrosion. Almost always an easy fix.

How to tell: Water from spigot at very bottom or valve-to-tank connection.
3

Inlet/Outlet Fittings

Common

Top connections loosen from thermal expansion. Corroded dielectric unions common.

How to tell: Water from top running down side. Mineral deposits or corrosion at connections.
4

Internal Tank Corrosion

Common

Depleted anode rod (3-5 years) leads to tank rust-through. Unrepairable. Average lifespan: 8-12 years.

How to tell: Water pools under tank, no source from valves. Rust stains. Tank 8+ years old.
5

Condensation

Common

New or freshly filled tanks cause condensation. Resolves in 24-48 hours.

How to tell: Recently installed. Moisture evenly on surface. Stops once heated.

How to Fix It

Tighten/Replace Drain Valve

$0-15
  1. 1Try tightening with wrench.
  2. 2If leaking, drain tank and replace valve ($8-15).
  3. 3Teflon tape threads. Upgrade to brass ball valve.

Fix T&P Issue

$15-350
  1. 1Check thermostat — 120°F.
  2. 2Test pressure. If high, need PRV ($200-350 installed).
  3. 3If backflow preventer present, add expansion tank ($40-60).
  4. 4Never cap a T&P valve.

Replace Water Heater

$800-2,000+
  1. 1Tank corrosion = replacement only.
  2. 2Standard 40-50 gal: $400-800 + $400-1,200 install.
  3. 3Tankless: $1,500-3,500, lasts 20+ years.

When to Call a Professional

Never cap T&P valve — explosion risk.

10+ year tank leaking from bottom = prepare for replacement.

Rust-colored hot water = depleted anode rod.

Gas heater near burner = shut off gas immediately.

How to Prevent It

Replace anode rod every 3-5 years ($20-50).

Flush tank annually.

Set thermostat to 120°F.

Install drip pan ($15-25).

Frequently Asked Questions

How long do they last?

Tank: 8-12 years, 15+ with anode maintenance. Tankless: 20+.

Can a leak be repaired?

Valves/fittings: yes, under $50. Tank corrosion: no, replace.

Is it dangerous?

Dripping valve: wasteful. Corroded tank: damage risk. Gas near burner: shut off.

Should I turn it off?

Yes. Power off (breaker/gas valve) and close cold water supply.

Related Guides

Water Heater From Bottom
Bottom diagnosis
Pipe Under Sink
Connection leaks
Basement Leaking
Water below
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