New water heater and the T&P valve is already leaking
Call the installer — this is warranty work
A valve that drips on a heater only weeks old has not worn out. Two things cause this, and both are the installer's to fix: the new install created a closed system with no expansion tank, or debris and thread sealant got into the valve seat during fitting.
How to tell it's this
- The heater was fitted in the last few months.
- A pressure-reducing valve or backflow preventer was fitted at the same time, or the meter was changed.
- There is no thermal expansion tank on the cold inlet — a small tank, usually blue or white, roughly the size of a football.
- It started within days of the install rather than gradually.
What to do
- Call whoever installed it before you pay anyone else. A drip this early is theirs to diagnose.
- Ask specifically whether the system is closed and whether an expansion tank was fitted. Many codes require one when a check valve or PRV is present.
- Keep the invoice and the manufacturer's paperwork. Tanks carry 6–12 year warranties, and the valve is covered too.
- Do not let anyone cap the valve to stop the mess while you wait for a callback.
What it costs
Expect to pay nothing. This falls under the installation warranty or the manufacturer's warranty. If an expansion tank turns out to be missing and code required one, fitting it is the installer's cost, not yours.
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 heater is several years old
The valve itself has failed →
Water is pooling under a brand-new tank instead
A new heater leaking underneath →
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.