Reliance water heater age by serial number
The serial number is on the rating plate on the tank. Reliance water heaters are built by State, so a serial from 2008 or later starts with the year and the week, and an older one starts with a letter for the month.
Decode a Reliance serial number
How to read a Reliance serial number
Reliance has used 3 serial formats. Find the one that matches the shape of your serial.
Year and week, first four digits
Skip a leading letter if there is one. The first two digits are the year and the next two are the week of that year.
Shape: four digits, then a letter and six digits, or nine more digits. Some serials carry one extra letter in front.
1210A002243 reads as week 10 of 2012 (around March).
Month letter, then two-digit year
The first letter is the month, A for January through M for December with the letter I left out. The two digits after it are the year.
Shape: one letter, two digits, then a letter and six digits or six to eight digits.
E07A135491 reads as May 2007.
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
State and Reliance used this layout for decades. A. O. Smith-branded heaters carry it only from July 2004, when the leading factory letter was dropped, to 2007.
Factory letter, month letter, two-digit year
The first letter is the factory. The second letter is the month, A for January through M for December with the letter I left out. The two digits after the letters are the year.
Shape: two letters, two digits, then more digits. Older plates print it in hyphenated groups.
GG03-1495366-S29 reads as July 2003.
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
Where to find the serial number
The rating plate is on the outside of the tank jacket. On gas models it is next to the gas control valve.
Newer plates print a build date under the serial number. When it is there, read it directly.
If the serial number does not decode
- Reliance water heaters are built by State Industries, which A. O. Smith has owned since 2001. The serial follows State’s formats.
- The manufacturer can confirm the date from the serial: Reliance registration, warranty or serial lookup.
What the age tells you
| Equipment | Typical service life |
|---|---|
| Tank water heater | 10 to 15 years |
| Tankless water heater | about 20 years |
About Reliance
Reliance water heaters are built on State’s production lines. State has been part of A. O. Smith since 2001, and recall notices list Reliance next to State and A. O. Smith with the same serial ranges.
Brands that share this serial system: State, A. O. Smith, Kenmore.
Questions and answers
Which characters in a Reliance serial number show the date?
Skip a leading letter if there is one. The first two digits are the year and the next two are the week of that year. This applies to units built since 2008.
Why does my Reliance serial number look different?
Reliance has used 3 serial formats: year and week, first four digits (built since 2008); month letter, then two-digit year (built until 2007); factory letter, month letter, two-digit year (built until mid-2004). The decoder tries each one.
Who makes Reliance water heaters?
Reliance water heaters are built by State Industries, which A. O. Smith has owned since 2001. The serial follows State’s formats.
Sources
- A. O. Smith Canada: frequently asked questions, reading the serial number (manufacturer): https://www.hotwatercanada.ca/faqs/
- A. O. Smith International: manufacturing date of a device (manufacturer): https://aosmithinternational.com/manufacturing-date-device/
- CPSC recall 19-029: A. O. Smith ultra-low NOx water heaters, serial ranges by build date (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2019/A-O-Smith-Recalls-Ultra-Low-NOx-Water-Heaters-Due-to-Fire-Hazard
- Building Intelligence Center: A. O. Smith water heater age (independent reference): https://www.building-center.org/a-o-smith-water-heater-age/
- CPSC recall: A. O. Smith, State, Reliance, Maytag and Apollo water heaters, serial prefixes by month (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2005/cpsc-ao-smith-recall-of-water-heaters
- CPSC recall: A. O. Smith gas water heaters, serial ranges for units sold November 2007 to January 2008 (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2008/ao-smith-recalls-gas-water-heaters-due-to-fire-and-carbon-monoxide-hazards
- Building Intelligence Center: State water heater age (independent reference): https://www.building-center.org/state-water-heater-age/
- CPSC recall: A. O. Smith gas water heaters built April to July 1991, serial prefixes MD91 to MG91 (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2012/certain-30-and-40-gallon-ao-smith-lp-and-natural-gas-water-heaters-voluntarily-recalled
- InspectAPedia: A. O. Smith water heater age (independent reference): https://inspectapedia.com/plumbing/AO-Smith-Water-Heater-Age-Manuals.php
Formats last checked against these sources on October 5, 2026. Found a serial that does not fit? Send a correction. How formats are verified: method and sources.