Marathon manuals are hosted at marathonheaters.com under "Documentation" and at rheem.com under the Rheem family brand library. Printed manuals ship with new units.
Where to download
- marathonheaters.com → Documentation → search by model number
- rheem.com — Rheem corporate hosts many Marathon documents
- Marathon tech support: 1-800-432-8373 — emails PDF manuals within hours
- Plumbing wholesaler — F.W. Webb, Ferguson can provide installation guides
Documents by model
- Standard Residential (MR40/50/55/66/75/85/105) — single installation and operation manual covers the line
- Heavy Duty (MHD40/50/75/85) — separate manual for 5500W element variants
- Lowboy / Mobile Home (MRH38/50) — distinct manual for short-height applications
Critical sections to read
- Electrical requirements and wiring diagram
- Initial fill-up procedure (prevent dry-fire)
- T&P valve test schedule
- Warranty terms and registration instructions
- Troubleshooting matrix (thermostat / element / ECO procedures)
Bottom line
Marathon manuals are concise — the composite tank doesn\'t need the lengthy maintenance sections that mainstream tank manuals devote to anode rod care. Installation is the most important section; once installed properly, Marathon needs minimal documentation reference.