Water heater leaking from the hot water outlet
Likely a repair
This is a fitting, not the tank. The hot outlet is the pipe carrying water away from the heater, normally on the left as you face it and hot to the touch. A leak here is the union, the flexible connector, or the threaded nipple it screws into.
The outlet pipe and the water in it can be 120 °F or hotter. Let it cool before touching it.
How to tell it's this
- The wet pipe is hot. The cold inlet beside it is not.
- You can trace the water up to a threaded joint, not to the tank shell.
- The top of the tank under the fitting is wet, but the jacket lower down is dry.
- It drips faster when hot water is running.
What to do
- Shut off the cold water to the heater first, then run a hot tap to drop the pressure.
- Dry the joint completely and watch it for ten minutes to confirm which fitting is weeping.
- Look for corrosion where copper meets steel. A dielectric union or a corroded nipple is a common cause and needs replacing, not tightening.
- Have a plumber remake the joint. Over-tightening a corroded nipple can snap it off inside the tank, which turns a $200 job into a replacement.
What it costs
With a plumber
Reseal or replace the leaking connector
$150–$400
installed
Part only
If a pro is already on site
$10–$50
the part itself
Typical US ranges for 2026, not quotes. Labour is 30–50% of an installed price, so where you live moves these numbers more than anything else does. Get two or three local estimates.
If that's not it
The wet pipe is cold, on the other side
The cold inlet is leaking →
Water is sitting on the tank top with no wet fitting above it
Water pooling on top →
Not sure which of these it is?
Answer four questions — where it's leaking, tank or tankless, gas or electric, and how
old it is — for a specific cause, a repair-or-replace call, and a cost.