Why is my water heater leaking?
Find the source first — a fitting you can fix, or a tank that must be replaced.
By The T.A.P. Team · December 2024 · 6 min read
A leaking water heater falls into two camps: a leak from a fitting, valve, or connection — often repairable — or a leak from the tank itself, which means the tank has corroded through and needs replacing. The first job is finding where the water is actually coming from. And because a failing tank can go from a drip to a flood, a leaking water heater is one to act on quickly.
- 1Shut off power/gas to the heater and the cold-water supply.
- 2Dry everything, then watch where water reappears.
- 3Check the top: cold and hot line connections.
- 4Check the T&P valve and the drain valve.
- 5Water from the tank base = a failed tank (replace).
First, make it safe and find the source
Turn off the heater (breaker for electric, gas control to "off" for gas) and shut the cold-water supply valve on top. Dry the whole unit and the floor, then watch. Where the water returns tells you almost everything — a top-of-tank leak is usually a fitting; a valve leak is the T&P or drain valve; water pooling from underneath usually means the tank itself.
Leaks you can often fix
Loose or corroded connections at the cold and hot water lines on top can sometimes be tightened or replaced. The drain valve at the bottom may just need closing fully or replacing if it drips. A leaking temperature-and-pressure (T&P) relief valve may be doing its job (relieving excess pressure) or may be faulty — but don't cap it; it's a critical safety valve.
The T&P valve: a safety you never plug
The T&P valve releases water if the tank's temperature or pressure gets dangerously high. If it's dripping, the cause might be high pressure (a pressure/PRV issue) or a bad valve — both need attention, but never plug or cap the valve. A blocked T&P valve on an overheating tank is genuinely dangerous.
When the tank itself is leaking
If water is coming from the bottom of the tank, internal corrosion has finally breached it — and there's no repair; the heater must be replaced. Tanks usually fail this way at the end of their life (see how long a water heater lasts). Replace it promptly before the slow leak becomes a burst tank and a flooded room. Consider a tankless while you're at it.
| Symptom | Likely cause | What to do |
|---|---|---|
| Water at top fittings | Loose line connection | Tighten/replace the fitting |
| Drip from the drain valve | Valve not closed / worn | Close fully or replace |
| Drip from the T&P valve | High pressure or bad valve | Check pressure; never cap it |
| Water from the tank base | Corroded tank | Replace the heater |
| Sudden large leak | Tank failure | Shut off water; call a pro now |
You can DIY
- Shut off power/gas and cold water
- Dry and locate the source
- Tighten a loose line fitting
- Close or replace a dripping drain valve
- Move items away from the leak
Call a pro
- A leaking tank (replacement)
- A dripping T&P valve
- High water pressure / PRV
- Gas heater repairs
- Any sudden or large leak
A dripping temperature-and-pressure relief valve is tempting to plug — don't. It's the safety that keeps an overheating tank from becoming a hazard. If it's leaking, find out whether it's excess pressure or a failed valve and fix the cause. And a leak from the tank base is always a replacement, never a patch — the corrosion won't reverse.
Hard water and aging tanks in DFW
North Texas's hard water accelerates the sediment and corrosion that eventually breach a tank, so local heaters tend to reach that leaking-tank stage on the earlier side. We repair fixable leaks and replace failed tanks across Plano, McKinney, and Frisco. See our plumbing team.
The short version
- A leaking water heater is either a fitting/valve leak (often fixable) or a failed tank (replace).
- Shut off power or gas and the cold-water supply, dry it, and watch where water returns.
- Top-of-tank leaks are usually loose line connections you can tighten.
- Never cap a dripping T&P relief valve — it's a critical safety.
- Water from the base means the tank has corroded through — replace it.
- Act fast: a slow tank leak can become a burst tank and a flooded room.
Water heater leaks — frequently asked questions
Water heater leaking?
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