Marathon Water Heater Age by Serial Number
Decode your Marathon serial number to find the manufacturing date, age, and full specs. Free and instant — no account needed.
Marathon Water Heater Age & Model Info
Brand: Marathon (pre-selected)
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Finding Your Marathon Serial Number
Check these four spots on your Marathon water heater
Common Locations
What to Look For
- White or metallic manufacturer sticker
- Labeled "Serial No." or "S/N"
- Typically 8–12 characters long
- Usually near the model number
Can't find it? Try removing access panels or checking behind the temperature dial.
Marathon Serial Number Examples
Don't worry if yours looks different — Marathon has multiple formats and our system can decode most variations.
About Marathon Water Heaters
Marathon water heaters are manufactured by Rheem and hold the distinction of being the only water heater in the industry backed by a lifetime tank warranty for residential use. First introduced in the late 1980s, the Marathon line was engineered to eliminate the primary failure point of traditional water heaters: tank corrosion. Instead of steel with a glass lining, Marathon uses a seamless, blow-molded polybutene plastic tank that cannot rust, corrode, or scale. This proprietary design eliminates the need for a sacrificial anode rod entirely, removing one of the most common maintenance items associated with conventional water heaters.
Marathon electric water heaters are available in tank capacities ranging from 50 to 105 gallons, covering both residential and light commercial applications. The thick foam insulation surrounding the polybutene tank dramatically reduces standby heat loss, contributing to lower operating costs compared to standard electric models. Heating elements and thermostats are conventional electric resistance components that are straightforward to replace when needed. Because the tank itself is warranted for life, many homeowners find that replacing the relatively inexpensive heating element or thermostat is far more economical than replacing the entire unit. Marathon is sold exclusively through Rheem professional contractors rather than retail channels, ensuring proper sizing and installation.
The serial number on Marathon water heaters follows a simple MMYY format for the first four digits, where the first two digits represent the production month (01 through 12) and the next two digits represent the two-digit production year. For example, a serial number beginning with 0189 indicates manufacture in January 1989. This straightforward encoding makes it easy to determine the exact age of any Marathon unit. Rheem provides technical support and replacement parts through their professional contractor network, and the company offers one of the most comprehensive warranty support programs in the residential water heating industry.