How old is my Reliance water heater?

By Dana Whitlock. Updated October 2026. Widely documented.

Reliance tanks built before about 2008 came out of State Industries, and their serials show it. A leading letter means an older tank: the letter is the month, followed by a two-digit year. A leading digit means a newer one, where the first two digits are the year and the next two the week.

Reliance is an A.O. Smith brand, and its code carries the Widely documented label here. The maker has confirmed the year-week reading in recall material, and inspector references line up on the older letter code, but Reliance does not publish decoding instructions of its own.

Where to find the label on a Reliance water heater

The label sits on the front of the jacket, a short way from the gas control or, on electric models, near the thermostat access cover. It is the sticker carrying the model number, the serial and the gallon capacity. A small flashlight and a dry rag are all you need. Do not pry off covers or reach behind the tank while it is running. If the label faces a wall, a phone camera slipped into the gap is safer than moving the heater.

How to read the code

For a serial such as 0833A032628, split off the first four digits: 08 is 2008 and 33 is the 33rd week, roughly mid-August. The A and the digits after it are a plant letter and a running count. For a serial such as D03304410, the D stands for April and 03 for 2003, so that tank was built in April 2003. The month letters skip I, so they run A to H for January to August, then J, K, L and M for September to December.

Real serials in this code

When the format changed

Reliance tanks were built by State Industries for years, and they followed State's habit of a one-letter month code until about 2008. After the switch, Reliance serials start with digits and carry no letter at the front, as an InterNACHI member pointed out when reading 0833A032628. The two layouts never overlap in a way that confuses the year, because one begins with a letter and the other with a digit. The install date is the harder question. For that, look for a permit sticker near the tank, a dated receipt, or ask Reliance's warranty verification page what coverage is left on the serial.

Who makes Reliance

Reliance is sold under A.O. Smith, whose name appears in the footer of the Reliance website. Its code twins are State (which built Reliance tanks before 2008) and A.O. Smith itself; Kenmore tanks from State share the older letter code too. American, U.S. Craftmaster and Whirlpool are A.O. Smith cousins with a similar year-week layout, though they adopted it decades earlier.

How sure is this?

Widely documented. Reliance doesn't publish this code; it comes from recall notices, service literature and inspector references. We tested the ao smith rules against 34 serials, 32 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with Reliance's serial lookup before you spend money on the answer.

Quick notes

• A seller's disclosure that says a tank is a certain age can be checked against the serial in seconds.
• Week 01 to 04 is January; week 49 to 53 is December. Use that to sanity-check a year-week reading.
• An electric Reliance tank with its age in the double digits deserves a look at the drain valve and base for rust before you spend on new elements.
• Reliance's warranty verification page works from the serial, so a sharp photo of the label is enough to check coverage before calling anyone.