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How old is my Lochinvar water heater?

Type the serial number from the Lochinvar label to see when it was built. Lochinvar units are built by A.O. Smith since 2011, so the serials follow that company's format.

Example

KJ1000130

KYear: K = 1993
JMonth: J = September

Built September 1993

33 years, 1 month old

Past typical life. Past the usual 6 to 12 year lifespan. Watch for rust-colored hot water, rumbling or popping from the tank, and moisture around the base.

Plan the replacement

Plan the replacement before it fails. A failed tank can release its full contents onto the floor.
Check the base and the fittings on top for moisture or rust now, and keep checking.
Know where the cold water shutoff above the tank is, so you can stop a leak quickly.
Some home insurers ask the age of the water heater, and in Florida a 4-point inspection flags tanks over 10 years. Check before you renew or buy a house.
Tank warranties usually run 6 to 12 years. Coverage usually counts from the install date or from a few months after the build date, so the build date is a good guide.

How this was read

The first letter, K, is the year on Lochinvar's chart.
The second letter, J, is the month: September.

Format: Lochinvar year and month letters. Sources: Lochinvar warranty by serial number (PDF), Building Intelligence Center: Lochinvar.

Reading a Lochinvar serial number

Before 2011 Lochinvar residential tanks used a year letter and a month letter, like Bradford White. Since A.O. Smith bought the company in 2011, they use year and week digits.

About Lochinvar

Lochinvar began as the Walter Vallett Company in 1939 and took the name Lochinvar Water Heater Corporation in Detroit in 1957.
The company moved to Nashville in 1970 and to a 360,000 sq. ft. headquarters and plant in Lebanon, Tennessee, in 2001.
A.O. Smith closed the purchase on August 26, 2011, paying $418 million in cash, including $28 million for the Lebanon headquarters and plant.

Sources: About Us | Lochinvar, A. O. Smith Corporation Form 10-K for fiscal 2011, A.O. Smith Acquires Lochinvar (Contracting Business, 2011)

Year and week

Used 2011 to today. Example: 1142N012345

Since 2011 Lochinvar residential tanks use the A.O. Smith year and week format, with a plant letter in the fifth position, like 1142N012345 for week 42 of 2011.

Worked example: 1142N012345 was built Week 42 of 2011 (around October), so it is 15 years old as of October 2026.

Sources: Lochinvar warranty by serial number (PDF), Building Intelligence Center: Lochinvar

Lochinvar year and month letters

Used 1979 to 2011. Example: KJ1000130

The first letter is the year and the second is the month, the same scheme Bradford White uses. Some year letters fit two dates 20 years apart.

Worked example: KJ-1000130 was built September 1993, so it is 33 years, 1 month old as of October 2026.

Year letter (first letter)
Letter	Year
A	1984 or 2004
B	1985 or 2005
C	1986 or 2006
D	1987 or 2007
E	1988 or 2008
F	1989 or 2009
G	1990 or 2010
H	1991 or 2011
J	1992
K	1993
L	1994
M	1995
N	1996
P	1997
S	1998
T	1979 or 1999
W	1980 or 2000
X	1981 or 2001
Y	1982 or 2002
Z	1983 or 2003

Month letter
Letter	Month
A	January
B	February
C	March
D	April
E	May
F	June
G	July
H	August
J	September
K	October
L	November
M	December

Sources: Lochinvar warranty by serial number (PDF), Building Intelligence Center: Lochinvar

Lochinvar recalls

Recalls from the U.S. Consumer Product Safety Commission that name Lochinvar. Whether a unit is included depends on its model and build date; the checker above flags matches.

Year	Recall	Hazard
2005	Robertshaw R110 gas valves on water heaters	Screws on the gas valve can break and leak gas, which can cause a fire or explosion.

Standing at the unit? Use your phone

Point your phone’s camera at this code. The scanner opens and reads the label for you.

Formats on this page were last checked against their sources in October 2026. Lochinvar is a trademark of its owner. This page is independent and not affiliated with or endorsed by Lochinvar. For warranty questions, contact Lochinvar directly.

Where the serial is on a Lochinvar

The rating label is on the front of the tank near the controls.

The label is a sticker on the side of the tank, usually above the gas valve or the upper thermostat cover. On units squeezed into a closet it often faces the wall, so a phone photo is easier than reading it by eye.