A 1991 through 2007 serial starts with a month letter and a two digit year, sometimes with a factory letter before the month.
The 2008 change moved the date code and made it more precise. Older Reliance serial numbers identify a month, while newer serial numbers with a date code identify a production week. In both formats, the complete printed serial is enough to find the date. A nine digit SAP barcode number is the exception: it contains no date code. The model number is optional and is not part of the date calculation.
First Decide Whether the Reliance Serial Starts with Digits or Letters
The opening characters tell you which rule to use. Do not treat the 00 in an older letter serial as if it were the start of a modern year and week code.
| Serial example | Date fields | Period | Date returned |
|---|---|---|---|
| 0833A032628 | 08 = year; 33 = week | 2008 onward | Production week 33 of 2008 |
| A00114092 | A = month; 00 = year | 1991–2007 | January 2000 |
| MA04A0001 | M = factory; A = month; 04 = year | 1991 through June 2004 | January 2004 |
Find the Age of Your Reliance Water Heater with Appliage
Copy the Number from the Tank, Not a Replacement Part
The Reliance rating label is fixed to the outside of the tank. On a gas water heater, look above or beside the gas control. On an electric model, check near an element access panel. The serial is on the tank label, not on a replacement gas valve, thermostat, or burner assembly.
The rating label is visible from outside the tank. Do not remove the gas control or an electrical cover to find it.
Include the first zero or letter when you copy Serial No. A missing zero shifts the year and week fields in a numeric serial. A missing letter can remove either the factory code or the month from an older serial.
Enter the Reliance Serial Number
Type the complete number into Appliage. A serial with a date code from 2008 onward begins with a valid YYWW code and produces a year, production week, and estimated age. A valid letter serial from 1991 through 2007 produces a manufacture month and estimated age. If the number is exactly nine digits, look for BUILD DATE or a separate date code on the rating plate.
The Reliance YYWW Rule from 2008 Onward
- Digits 1–2 two digit year
- Digits 3–4 production week
- Character 5 onward tank identifier
For example, the serial number 0833A032628 has three parts: 08 | 33 | A032628. The first pair means 2008, the second pair means production week 33, and A032628 identifies the tank. Therefore, the manufacture date is production week 33 of 2008.
| Week code | Meaning |
|---|---|
| 01–09 | Production weeks 1 through 9; the first zero must be kept |
| 10–53 | Production weeks 10 through 53 |
| 00 | No production date because there is no week 0 |
| 54–99 | No production date because the value is outside the week range |
The Older Reliance Letter Rule
From 1991 through 2007, the month appears as a letter before the two digit year. For example, the serial number A00114092 starts with A | 00. A means January and 00 means 2000. Therefore, the manufacture date is January 2000.
Some tanks add a factory code before the date. For example, in the serial number MA04A0001, the first M identifies the factory, A means January, and 04 means 2004. Therefore, the manufacture date is January 2004.
The two letter opening appears through June 2004. The factory letter does not supply any part of the date; it only moves the month and year one position to the right.
The Month Letters Changed after 2002
Reliance used I for September through 2002. From 2003 onward, the month sequence omits I: J becomes September, K becomes October, L becomes November, and M becomes December. The year period must be established before one of these later month letters can be interpreted correctly.
| Month | 1991–2002 | 2003–2007 |
|---|---|---|
| January | A | A |
| February | B | B |
| March | C | C |
| April | D | D |
| May | E | E |
| June | F | F |
| July | G | G |
| August | H | H |
| September | I | J |
| October | J | K |
| November | K | L |
| December | L | M |
What Happens at the Ends of the Two Periods?
For example, the serial number A90123456 can be divided as A | 90 | 123456. A would normally mean January and 90 would mean 1990. However, the documented Reliance letter format begins in 1991. Appliage therefore returns no age instead of assigning January 1990.
A letter serial that points to 2008 is also outside its documented period because Reliance had changed to the year and week format. A YYWW serial returns no age when its week is 00 or above 53. A nine digit SAP barcode number also returns no date because those nine digits identify the unit but do not contain YYWW.
Why Reliance Uses State and A. O. Smith Serial Systems
Reliance is the brand printed on the tank, while the date system changed with the companies that made and serviced the product. Reliance tanks from 1991 through 2007 came from the same Ashland City operation as State water heaters. Federal recall records place both brands in the same month letter and two digit year tables.
A. O. Smith service material places Reliance in the shared year and week system from 2008 onward. This is why an older Reliance serial begins with letters while a newer one begins with four date digits.
Select Reliance when that name appears on the tank. If the rating plate says A. O. Smith instead, use the A. O. Smith water heater guide.
Sources
- A. O. Smith 2024 Service and Warranty Guide. The manufacturer guide publishes YYWW and lists Reliance in the shared service system.
- A. O. Smith serial number change notice (2016). The notice says the barcode captures only the nine digit SAP serial and does not include the date code.
- CPSC Reliance water heater recall 06-002. The federal notice names Reliance models in the shared month prefix table used during 2004 and 2005.
- CPSC water heater control recall 04-128. The registration record lists Reliance with the State letter prefixes used in 2002 and 2003.
Appliage is an independent appliance age research tool. It is not affiliated with or endorsed by Reliance or A. O. Smith. See how the evidence standard works on our About page.
