How old is my Reliance water heater?

Serial number age decoder for Reliance tank water heaters: 8 format eras, the decode rule in plain English, transcribed tables, and the official lookup.

• Reliance water heater serial numbers in the 2008 to present format encode the year as digits 1-2 (YY) after optional leading S and the week as digits 3-4 (source: building-center.org).
• Example: serial 1210A002243 decodes to week 10 of 2012.
• Reliance water heater serial numbers in the before 2010 format encode the year as digits 2-3 = FISCAL year (Oct 1 - Sep 30); for A/B/C (Oct-Dec) subtract 1 for calendar year (A91 = Oct 1990) and the month as letter 1, fiscal table A=Oct..M=Sep (I skipped) (source: building-center.org).
• Example: serial L92441351 decodes to August 1992.
• Reliance water heater serial numbers in the before 2010 format encode the year as digits 2-3 = fiscal year (see style 1) and the month as letter 1, fiscal table A=Oct (source: building-center.org).
• Example: serial C91A136750 decodes to December 1991.
• Reliance's official lookup at reliancewaterheaters.com returns warranty / registration lookup.

Format eras

• before 2010 VERIFIED
  A########digits 2-3 = FISCAL year (Oct 1 - Sep 30); for A/B/C (Oct-Dec) subtract 1 for calendar yea
• before 2010 VERIFIED
  A##A######digits 2-3 = fiscal year (see style 1)
• before 2010 VERIFIED
  AA########digits 4-5 = fiscal year
• before 2010 VERIFIED
  A##A######digits 2-3
• 2008 to present VERIFIED
  ####A######digits 1-2 (YY) after optional leading S
• 2008 to present VERIFIED
  ####A######digits 1-2 (20YY)
• before 2008 VERIFIED
  AA##A######digits 3-4
• 1970 to 1979 VERIFIED
  A##-A-##-######2 digits between hyphens (78)

How to read the serial

before 2010 formatVERIFIED

Shape A######## · example L92441351 · confidence medium

Year

digits 2-3 = FISCAL year (Oct 1 - Sep 30); for A/B/C (Oct-Dec) subtract 1 for calendar year (A91 = Oct 1990)

Week or month

month = letter 1, fiscal table A=Oct..M=Sep (I skipped)

Example: serial L92441351 decodes to August 1992.

before 2010 formatVERIFIED

Shape A##A###### · example C91A136750 · confidence medium

Year

digits 2-3 = fiscal year (see style 1)

Week or month

month = letter 1, fiscal table A=Oct

Example: serial C91A136750 decodes to December 1991.

before 2010 formatVERIFIED

Shape AA######## · example AJ03123456 · confidence medium

Year

digits 4-5 = fiscal year

Week or month

month = letter 2, fiscal table A=Oct

Plant

letter 1 (factory, unpublished)

before 2010 formatVERIFIED

Shape A##A###### · example E07A135491 · confidence medium

Year

digits 2-3

Week or month

month = letter 1 (A=Jan..)

Example: serial E07A135491 decodes to May 2007.

Listed under A.O. Smith in the source; Reliance is named in that format's family and the corporate link is an estimate, not a checked fact.

2008 to present formatVERIFIED

Shape ####A###### · example 1210A002243 / S1318 F000046 / 1836111786352 · confidence high

Year

digits 1-2 (YY) after optional leading S

Week or month

week = digits 3-4

Plant

letter after the 4 date digits (unpublished)

Example: serial 1210A002243 decodes to week 10 of 2012.

Listed under A.O. Smith in the source; Reliance is named in that format's family and the corporate link is an estimate, not a checked fact.

2008 to present formatVERIFIED

Shape ####A###### · example 1211A018632 · confidence high

Year

digits 1-2 (20YY)

Week or month

week = digits 3-4

Plant

letter 5

Example: serial 1211A018632 decodes to week 11 of 2012.

before 2008 formatVERIFIED

Shape AA##A###### · example AF04A093001 / GG03-1495366-S29 · confidence medium

Year

digits 3-4

Week or month

month = letter 2 (A=Jan..)

Plant

letter 1

Example: serial AF04A093001 decodes to June 2004.

Listed under A.O. Smith in the source; Reliance is named in that format's family and the corporate link is an estimate, not a checked fact.

1970 to 1979 formatVERIFIED

Shape A##-A-##-###### · example A20-H-78-015482 · confidence medium

Year

2 digits between hyphens (78)

Week or month

month = letter between hyphens (H=Aug)

Example: serial A20-H-78-015482 decodes to August 1978.

Listed under A.O. Smith in the source; Reliance is named in that format's family and the corporate link is an estimate, not a checked fact.

Where the data plate is on a water heater

The rating plate is a large label on the side of the tank near the top or beside the control. The serial is printed on it, often beside the model number and the ANSI standard line.

General guidance, not brand-specific: the owner's manual or the installer can point to the exact spot. See the data plate guide.

For scale only: the InterNACHI Standard Estimated Life Expectancy Chart for Homes lists Water Heater (conventional) at 6 to 12 years of expected service (nachi.org). That chart is a guideline, not a prediction for your unit.

What we could not confirm

• Reliance is treated as sharing A.O. Smith's format because the source lists it in that family; the corporate relationship itself is an estimate.
• The before 2010 format is documented but not decodable here: example AJ03123456 does not decode with the derived engine.
• Style 4 (1211A018632) = A.O. Smith YYWW. Styles 1-3 use a FISCAL-year month table (A=Oct) unlike State/AO Smith letter styles.

Sources

• https://www.building-center.org/a-o-smith/
• https://www.building-center.org/reliance-water-heater-age/
• img: RELIANCE-1-WH-Serial-Number.jpg (last update Jul-2012)
• img: RELIANCE-2-WH-Serial-Number.jpg
• img: RELIANCE-3-WH-Serial-Number.jpg
• img: Reliance-Water-Heater-Style-4.png
• https://www.reliancewaterheaters.com/support/warranty-verification.htmlofficial

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