Seisco® Water Heaters

The date of production/manufacture or age of Seisco® Water Heater(s) cannot currently be determined from the serial number.

Serial number styles/formats found are:

Style 1: A602 36471

SEISCO no longer in business/discontinued effective December 15, 2017.*

First U.S. patent recorded in June, 1993, with later patents following in 1999, 2000, 2001, & 2009*

Prior to January, 2008 Seisco products were made by Microtherm, Inc.*

Microtherm, Inc. was liquidated on December 31, 2007*

SEISCO International Limited was founded January 1, 2008 and became the trademark and patent holder for the SEISCO family of products.*

A.O. Smith acquired SEISCO circa 2017.*

Despite many apparent accolades from industry sources and special recognition from several government agencies including PATH, HUD, NAHB Research Center, NREL, TVA, DOE, and EPRI, Seisco brand products were discontinued effective December 15, 2017 based on an intra-company news alert post published November 14, 2017 by distributor Hydro Pump Co. (1) , and no longer available per distributor (2)*

A.O. Smith will honor Seisco parts and product warranties for as long as they are in effect.*** (10-year limited/prorated warranty on residential products, and 5-year limited/prorated warranty on commercial products.) (3)*

The Seisco website ( remains published and accessible**; however, Technical, Service, & Sales inquiry emails listed on the company website are currently directed to A.O. Smith points of contact (*

Google maps search indicates company listed physical address as "Permanently Closed" *

* Information reasonably believed accurate based on extensive research conducted 10/03/2022.

** as of 10/03/2022

*** According to Hydro Pump Co. website posting (




Style 1: A602 36471

A Microtherm, Inc. style which indicates this unit was manufactured prior to the Microtherm, Inc. liquidation of December 31, 2007 (see data plate image of popular RA28 model below)

Every effort is undertaken to offer you correct and concise information to assist you in determining the age or manufacture date of water heating equipment. Anytime anyone is dealing with numbers and letters in determining data, mistakes and misinterpretation are bound to happen. For this reason if you find during your research that we may have erred please contact us. In addition perhaps you have come across a brand, model or serial number format that we have not addressed. Contact us with your concerns or new submissions. Please include all pertinent information including clear and legible pictures of data/nomenclature plates.