Water heater leaks fall into four categories by location. Most are repairable; tank body leaks mean replacement.
1. T&P relief valve discharging
Water flowing from the T&P discharge tube is usually thermal expansion, not a failed T&P.
- Cause: closed plumbing system + no expansion tank. Hot water expands; pressure rises; T&P relieves
- Fix: install expansion tank on cold supply line
- Also check: house pressure regulator (should be 50-80 PSI)
- If T&P still drips after expansion tank, replace T&P valve ($15-25)
2. Fitting leaks at top of tank
- Cold inlet union or hot outlet union
- Tighten with two pipe wrenches
- Replace washer or apply fresh Teflon tape if persistent
- Dielectric union failure — replace ($25-40)
3. Drain valve leak
- Plastic OEM drain valve seized partially open
- Tighten with channel-lock pliers
- Best fix: drain tank and replace with brass ¾" ball valve ($15-20)
4. Tank body leak (catastrophic)
- Symptom: water pooling under or around the tank body itself, not from fittings
- Cause: internal corrosion through the glass-lined steel tank
- Fix: none — tank is end-of-life. Replace the water heater
- Prevention: anode rod replacement every 4-7 years
Don\'t-skip diagnostic step
Wipe everything dry. Place paper towels under suspected leak points. Wait 2-4 hours. Identify exactly where water reappears. This tells you which fix to pursue.
When tank body leak means replacement
| Unit age | Recommendation |
|---|---|
| 0-6 years (under warranty) | Warranty replacement from manufacturer |
| 6-10 years | Replace; consider stepping up to longer warranty tier |
| 10+ years | Replace; consider Marathon composite (lifetime) or heat pump (IRA credit) |
Bottom line
Identify leak location first. T&P discharge → install expansion tank. Fitting leaks → tighten or re-seal. Drain valve → upgrade to brass ball valve. Tank body → replace the water heater. See leaking from bottom for the specific tank-failure scenario.