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 State serial number
How to read a State serial number
YYWW… (2008+), 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 |
|---|---|---|
S1318F000046 | S is skipped; 13 = 2013, 18 = week 18 (late April/early May) | Week 18 of 2013 (around May) |
C05123456 | Older style: C = March, 05 = 2005 | March 2005 |
- The Energy Trust of Oregon decoder (opens in a new tab) gives both formats for State: a month letter followed by a two-digit year on older heaters, and a serial of usually 11 characters (12 with a leading letter) with year then week on newer ones.
- Ignore a single letter at the start of a newer serial, as with A. O. Smith.
- State Select is a State product line, so the same code applies.
Format source: Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also Building Intelligence Center: State water heater age (opens in a new tab).
What to do with the date
- Check the warranty. Enter the serial number in the State warranty verification (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 State guides cover codes, lights, leaks and no-hot-water problems.
Common questions
Is State Select a different manufacturer?
No. State Select is a State line, built by A. O. Smith, and its serial uses the same date code.
How do I tell the old and new State formats apart?
If the first character is a letter followed by two digits and the serial is short, it is usually the older month-letter code. If the serial starts with four digits, or one letter and then four digits, read those digits as year and week.
Other brands: Bradford White · A. O. Smith · Rheem · Whirlpool · American Water Heater · Rinnai · all brands