Marathon Water Heater Age Lookup
Marathon is Rheem's lifetime-warranty electric heater with a plastic tank that won't rust. Enter your serial number to confirm the manufacture date and how old it is. Free and quick.
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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.
Where to find the serial
Marathon water heaters are distinctive - they have a tan or beige plastic jacket rather than the painted metal exterior of most tanks. The rating plate is on the side of the jacket and the serial is in a black bordered box labeled SERIAL NO. Marathon is the only brand with a polybutene plastic tank, so the labeling style is unique to this line.
What the serial actually looks like
Why the age is worth knowing
Marathon has a lifetime tank warranty (the tank itself cannot rust because it's plastic), so age is really about the heating elements, thermostats, and the foam insulation degrading. A 30-year-old Marathon with replaced elements is still going strong in plenty of basements. The lifetime warranty is transferrable to subsequent homeowners.
Quick answers for this brand
Does Marathon really have a lifetime tank warranty?
Yes, the Marathon polybutene plastic tank carries a non-prorated lifetime warranty for the original residential owner and a 10-year warranty if installed in a commercial setting. The warranty covers tank replacement if the tank itself ever fails. Heating elements and thermostats have shorter coverage (6 years) since they're standard replaceable parts.
Why don't Marathon tanks need an anode rod?
Anode rods exist to sacrifice themselves to corrosion in steel tanks. Marathon's polybutene plastic tank cannot rust or corrode, so the entire concept doesn't apply. This eliminates the most common maintenance item for traditional tanks and is the reason Marathon can offer a lifetime warranty.
Are Marathon water heaters only electric?
Yes, Marathon is electric-only. The polybutene tank construction can't handle the higher temperatures of a gas burner without softening, so there's no gas version. If you need a gas tank with similar longevity, look at stainless steel commercial units instead.
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