Where to look: Rating plate on the side of the tank jacket. Read it from the outside. If the label isn’t visible without removing a panel, don’t open the unit; use the installation paperwork or ask the installer.
Decode a A. O. Smith serial number
How to read a A. O. Smith serial number
YYWW… (2008+), YYMM… or month letter + YY (older) Current: the first four digits (after any single prefix letter) are YY then WW, year and production week; units built before 2008 use YY then MM, year and month. Older codes: a month letter A–M (no I) followed by a two-digit year, sometimes after one leading character.
| Example serial | How it reads | Built |
|---|---|---|
1210A002243 | 12 = 2012, 10 = production week 10 (early March) | Week 10 of 2012 (around March) |
U0106413635 | U is skipped; 01 = 2001, 06 = June | June 2001 |
2C062938405 | Older style: 2 is a leading character, C = March, 06 = 2006 | March 2006 |
- A. O. Smith’s serial number FAQ (opens in a new tab) says to ignore any letter at the start. From 2008 the two digits after the year are the production week; before 2008 they are the month. Its example, U0106413635, is June 2001.
- Some older serials use a leading character, then a month letter and a two-digit year instead: the City of Palo Alto’s age guide (opens in a new tab) reads 2C062938405 as March 2006. The decoder handles both styles.
- The same scheme is used on State and Reliance tanks, which A. O. Smith also builds. American, Whirlpool and U.S. Craftmaster tanks use a year-and-week code with no leading letter.
- A week number tells you the season rather than the exact day; the decoder shows the month that week falls in.
Format source: A. O. Smith Canada: FAQs (reading the serial number) (opens in a new tab); also City of Palo Alto Utilities: check your water heater’s age (opens in a new tab).
What to do with the date
- Check the warranty. Enter the serial number in the A. O. Smith warranty validation (opens in a new tab). Coverage depends on the model and the build or installation date.
- Weigh repair against replacement. Age is one factor; leaks from the tank, rusty hot water and repeated failures matter more. See how long water heaters last and the repair-or-replace notes on the main decoder page.
- Troubleshoot by brand. Our A. O. Smith guides cover codes, lights, leaks and no-hot-water problems.
Common questions
My A. O. Smith serial is 1305… Is that May 2013?
No. For heaters built from 2008, 05 is the fifth production week, so around the end of January or early February 2013. Only pre-2008 codes use the month.
Does this work for A. O. Smith tankless units?
A. O. Smith documents the format for its water heaters generally. If a tankless serial doesn’t decode, check the label for a printed date or use the warranty validation tool.
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