Brands that use this code
A.O. Smith owns State (announced 2001), American Water Heater (2006) and Lochinvar (2011). CPSC’s 2018 recall notice applies the same year-and-week rule to heaters sold as American, A.O. Smith, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool. Kenmore and Whirlpool water heaters have had other makers over the years, so check the maker’s name in the small print on the plate. More: American, Reliance, Whirlpool and Kenmore. Lochinvar tanks use their own code: see Lochinvar water heater age.
Basis: official (CPSC recall 19-029); ownership dates from A.O. Smith releases as reported by Building Intelligence Center.
Where the serial number is
| Model | Where to look |
|---|---|
| A.O. Smith gas | On the data plate next to the gas control valve/thermostat |
| A.O. Smith sold at Lowe’s | Possibly on the label near the bottom of the heater |
| State | On the nameplate on the side of the unit |
Basis: official (CPSC recall 19-029; A.O. Smith at Lowe’s owner center; State Water Heaters).
Serials from about 2008 on: year and week
CPSC’s 2018 A.O. Smith recall notice: “the first four digits represent the year and week of production.”
| Serial starts | Year | Week | Built |
|---|---|---|---|
| 1210A002243 | 2012 | 10 | early March 2012 |
| 0833A032628 | 2008 | 33 | mid-August 2008 |
| 1836111786352 | 2018 | 36 | early September 2018 |
| 1805 to 1809 | 2018 | 5–9 | about February 2018 (CPSC 19-030 range) |
Basis: official (CPSC 19-029 and 19-030, both US recall notices). A.O. Smith’s European site describes the same rule for its European products (2037 = week 37 of 2020); we use it only as supporting evidence. Examples: Building Intelligence Center and a Reliance/State serial posted on the InterNACHI forum.
If a letter comes first (for example S1318F000046), skip it and read the first four digits: 2013, week 18.
Older serials: month letter and year
| Letter | Month | Letter | Month |
|---|---|---|---|
| A | January | G | July |
| B | February | H | August |
| C | March | J | September |
| D | April | K | October |
| E | May | L | November |
| F | June | M | December |
There’s no I. Basis: official (CPSC recall 06-002, which lists “Jan-04 - MA04 or AA04 or A04” through “Jul-05 – G05”).
Which letter to read depends on the layout:
| Layout | Read | Example | Built |
|---|---|---|---|
| Letter + 2 digits (A.O. Smith from about July 2004; State for longer; used until about 2008–2010) | 1st letter = month, digits = year | L07A071460 | November 2007 |
| 2 letters + 2 digits (A.O. Smith before about July 2004) | 1st letter = a code (not the date), 2nd = month, digits = year | MD91… | April 1991 |
Basis: official (CPSC 08-241 lists L07A and M07A serials for heaters sold November 2007 to January 2008; CPSC 06-002 shows the switch to single-letter codes from July 2004; CPSC’s 1991 notice covers serials beginning MD91 to MG91, made April 16 to July 9, 1991).
A correction to one popular chart: InterNACHI’s dating chart gives J as October. CPSC’s official serial table (J04 = September 2004) shows J is September; our table follows CPSC.
American Water Heater units used year + week even before A.O. Smith bought the company in 2006 (InterNACHI’s chart: “8906xxx= made in the 6th week of the year 1989”). More: American water heater age.
Recalls to know about
These CPSC recalls name A.O. Smith or State heaters. Most used the serial date code to define which heaters were affected:
| Recall | What | How to tell (serials or codes covered) |
|---|---|---|
| CPSC 19-029 (Nov 2018) | Ultra-Low NOx gas water heaters: fire hazard | First four digits 1115 to 1631 (made April 2011 to August 2016) |
| CPSC 19-030 | 30-gallon gas water heaters sold only at Lowe’s: fire hazard | First four digits 1805 to 1809 |
| CPSC 15-155 (Jun 2015) | John Wood brand 50- and 70-gallon oil-fired water heaters, recalled by A.O. Smith: “The water heater’s combustion chamber can be misaligned and heat the exterior walls of the water heater instead of the water.” Fire and burn hazards. About 250 units | JW517: serials 1349A021678 through 1503A016643. JW717: serials 1421M001517 through 436M000040 (as printed by CPSC) |
| CPSC 08-241 (Apr 2008) | 75-gallon natural and propane gas water heaters with “A.O. Smith” or “State” on the side, sold November 2007 to January 2008: flue gas can get too hot and exhaust can leak into the room, fire and carbon monoxide hazards. About 1,500 units | A.O. Smith FCG-75 300 and FCG-75 301; State GS6 75 XRR S and GS6 75 CRR S; serials L07A071460 to L07A144966 or M07A009387 to M07A072884 |
| CPSC 06-002 (Oct 2005) | 75-gallon propane gas water heaters with “A.O. Smith,” “Reliance,” “Apollo,” “State,” or “Maytag” on the side: “The water heaters can accumulate soot on the burners, posing a fire hazard.” About 5,000 units | A.O. Smith models BT-80-271, FCG-75-271, PCG-75-271; State models GS675CRRS, GS675CRRSD, SBS7576PE, SBS7576PED, SBS7576PECGA, SBS7576PECGAD (other brands’ models on the notice). Made January 2004 to July 2005: serials beginning MA04, AA04 or A04 (January 2004) through G05 (July 2005) |
| CPSC 04-128 (Apr 2004) | White-Rodgers LP and convertible gas water heater controls on several brands, including AO Smith, Reliance and State: soot can build up on the burner, a fire hazard. 88,000 units | Date codes 0240 to 0329, a four-digit code stamped on the control (not the heater serial) |
| CPSC 92-016 (Nov 1991) | A.O. Smith FSG and PGX 30- and 40-gallon natural and LP gas water heaters: oversized flue baffles “may produce unacceptably high levels of carbon monoxide” | Serials beginning MD91, ME91, MF91 or MG91 (made April 16 to July 9, 1991) |
| CPSC 80-042 (Dec 1980) | LP gas water heaters with White-Rodgers thermostats from several makers, sold between 1961 and 1980, including A.O. Smith brand names (such as A.O. Smith, Glascote, Permaglas and Signet) and State Industries brand names (such as Sentry, President and Censible): the thermostat’s safety valve could stick open and let LP gas escape, an explosion hazard. About 600,000 units, all makers | An LP gas heater sold under a name on the notice between 1961 and 1980 |
Basis: official (CPSC notices in the sources). Old recalls may have closed, and the phone numbers and web addresses in them may no longer work. Always check the exact model on the notice, and run the model through our recall check.
Boilers too. Two Lochinvar recalls also cover A.O. Smith- and State-brand condensing boilers, combi boilers and packaged systems, which can emit carbon monoxide: CPSC 20-141 (June 2020; sold after August 2016, serials 103475818 to 115078306) and CPSC 24-018 (November 2023; A.O. Smith models starting ACB, State Industries models starting SCB, serials 125325485 to 134830284). Details: Lochinvar recalls.
If you can’t read it
Many newer plates print the date. Otherwise, contact A.O. Smith or State technical support (877-552-0010) with the model and serial number.
What the age means
A.O. Smith says traditional tank water heaters last 8 to 12 years and tankless models 15 to 20. Across published sources a tank typically lasts about 11 years (range 8 to 15); see how long water heaters last.
Comparing quotes? See what a new water heater costs installed. For the heating and cooling side of the house, the furnace or air conditioner’s serial carries a date too: Goodman, Carrier and Bryant, Trane and American Standard.
Limitations
- We couldn’t find the exact date A.O. Smith and State switched to the year-and-week code. The latest letter-coded units in CPSC records were sold into January 2008, the earliest year-and-week serial we found is from week 33 of 2008, and Building Intelligence Center says one letter style was discontinued “somewhere between 2008-2010”. The checker reads a month letter with a year up to 2010 as the older code.
- Week numbers give the week, not the day; we show the month that week falls in.
- A.O. Smith’s own published statement of the week rule is on its European site. For US models our official source is CPSC’s notice covering 2011–2016 production, and the 2018 serials in CPSC 19-030 fit the same code; we found no US A.O. Smith page that states it.
Checked against the sources below on 30 September 2026.
