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Why is my water heater leaking?

Where the water appears on a water heater is the whole diagnosis: top leaks are usually fittings you can see and reach, bottom leaks split between a valve doing its job and a tank at the end of its life.

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What it usually is

  1. Loose or corroded inlet and outlet fittings on top

    The cold-in and hot-out connections weep at their threads as sealant ages. Water runs down the jacket and pools underneath, imitating a bottom leak — always check the top first.

  2. The temperature and pressure relief valve discharging

    A T&P valve that drips is often responding to real overpressure — thermal expansion in a closed system — rather than failing. A steady drip from its discharge pipe is a message, not a malfunction.

  3. The drain valve at the base seeping

    The plastic drain spigot loosens or fails to seat after a flush. A hose cap on its threads is a legitimate stopgap while a replacement valve is arranged.

  4. Tank corrosion — the terminal one

    Water seeping from under the jacket with no wet fitting above it means the glass lining has failed and the steel is rusting through. Tanks do not get repaired; they get replaced, on your schedule or theirs.

Safety first: A T&P valve discharging hot water forcefully, or any bulging of the tank, means shut off the cold inlet and the heat source and call the same day.

What you can check yourself

Dry everything, then lay paper towels at the suspect spots and identify the true source in an hour. Snug (do not crank) a weeping fitting. Lift and snap shut the T&P lever once to reseat it; if it keeps dripping, note whether your home has a pressure regulator or check valve. For tank-seam leaks, close the cold inlet valve and start planning.

When it’s a job for a pro

T&P discharge tied to thermal expansion needs an expansion tank — a plumber sizes it in one visit. A corroding tank is a replacement conversation; ten years is the age where repair money stops making sense.

Fitting and valve repairs typically run $100 to $300; an expansion tank $150 to $350 installed; tank replacement commonly lands between $1,100 and $2,200 installed.

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