Why is your water heater leaking, and what does the fix cost?

Q: Why is your water heater leaking, and what does the fix cost?

Water pooling under a water heater comes from one of four places, and the cost depends entirely on which. A leaking relief valve is $100 to $250 to replace, a drain valve $100 to $200, a loose fitting can be as little as $50, and a corroded tank cannot be repaired at all. Figures from Fixr (August 2025); the diagnosis follows This Old House (May 2026).

The four sources, and what each costs

This Old House names three places a tank water heater leaks from; the fourth is the one that decides everything.

Source of the leak	What it needs	Cost	Source
Loose inlet, outlet or fitting	Tighten or reseal	from $50	Fixr
Drain valve	Replace the valve	$100 to $200	Fixr
Temperature and pressure relief valve	Replace the valve	$100 to $250	Fixr
Heating element gasket, electric units	Replace the element	$200 to $750	Fixr
The tank itself, corroded through	Nothing. Replace the heater	$900 to $3,000	Fixr

The first four are ordinary repairs. The fifth is the end of the appliance, and telling them apart before you pay anyone is the point of this page.

How to find out which one it is

This Old House's method, in order:

Turn off the power or gas and the cold water supply.
Examine every connection and fitting for moisture or drips.
Look for rust on the outside of the tank.
If the source is not obvious, dry the tank and the floor completely, then wait and see where water reappears.

Step four is the one people skip. This Old House's plumbing expert Richard Trethewey is blunt about the method: "Leaks can be tricky. You've just got to put your head down there and see what's going on." Dry it, take a flashlight, get on the floor and trace the water back to where it starts. Water runs down the side of a tank and pools at the base regardless of where it came from, so the puddle tells you nothing about the source.

Why the tank is the one that ends it

Trethewey explains what the tank actually is: "This is a steel tank with a glass lining. People think it's like a thermos bottle, it isn't. It's just a glass lining that's been baked onto the steel." Once that enamel cracks or wears through, water reaches the steel and corrosion starts from the inside.

Fixr puts tank repair at $250 to $1,000 and tank replacement at $600 to $2,000, and states plainly that corrosion damage cannot be undone. A rusted-through tank is replaced, not patched. Signs This Old House lists: visible rust on the outside of the tank, and rust-coloured water.

The anode rod is the part that is supposed to prevent exactly this, at $125 to $300 a time.

The relief valve trap

This is the case worth knowing about, because the obvious repair is often the wrong one.

A dripping temperature and pressure relief valve looks like a faulty valve. Sometimes it is. But This Old House documents a project where the homeowner, Dan, had been emptying a bucket under his relief valve three times a day and had already replaced three valves. Trethewey's reaction: "If you've replaced three of them, it makes me suspect that it's doing its job exactly. That we're building up 150 pounds of pressure somehow."

The real cause was a pressure-reducing valve on the main water line acting as a check valve. Water expands when it is heated, and with no way back into the city supply the pressure had nowhere to go. Installing a potable-water expansion tank dropped the pressure immediately and the dripping stopped.

What that means for your quote. A relief valve that drips is releasing pressure, which is its job. Before paying to replace it a second time, ask whether the house has a pressure-reducing valve or a check valve on the main. If it does, the fix is an expansion tank at $40 to $150 (This Old House) or $150 to $400 (Fixr), not another valve.

This Old House also warns against the opposite mistake: never cap or block a persistent drip. Interfering with a relief valve that is doing its job creates a dangerous pressure situation inside the tank.

What a leak costs if you leave it

This is the reason not to let it run. This Old House prices water damage repair from a failed unit at $500 to $2,500, and after-hours or weekend emergency service at $200 to $500 on top of a normal installation.

Our arithmetic, stated as such: a $150 valve job done on a weekday against a failed tank replaced on a Saturday with a flooded floor is roughly $150 against $1,400 plus $200 to $500 plus up to $2,500. Neither source stacks the figures this way; the individual numbers are theirs.

When to call someone and when not to

Fixr's repair figures assume a professional. Tightening a visibly loose fitting is within reach of most homeowners. Everything involving the relief valve, the gas connection or the heating elements is not: This Old House's maintenance guidance is explicit that work on gas lines, heating elements and safety devices belongs with a licensed professional, and that on older units disturbing worn parts can create new problems.

If the unit is past 10 years and the leak is anywhere near the tank body, the honest question is not what the repair costs but whether to repair or replace at all.

Sources

Price figures are national US ranges from the sources above as of the date shown. Your local price depends on labor rates, permits and site conditions. Read how we get our numbers.