Rheem Marathon non-metallic electric tank (MR40, MR50, MR85, point-of-use): quick sheet

Covers: Marathon residential electric tanks (e.g. MR40245C, MR50245C, MR40230, CMR85238) and point-of-use MR20230, MR15120.

Cross-checkedBrands: Rheem3 components

Seamless blow-molded polybutene tank wrapped in filament-wound fiberglass with a polyethylene shell: no anode rod, no rust. Lifetime limited tank warranty for residential use when registered within 90 days. Elements and thermostats are the usual service parts.

Safety first

Turn off the breaker and verify zero volts before touching elements, thermostats or terminals; 240 V tank and tankless units can be lethal.
Never energize an element without water around it (dry fire).
Do not remove or plug the T&P relief valve; its discharge line must run to a safe spot.

How it works

Two 4,500 W elements (non-simultaneous) on 240 V with upper and lower thermostats and an ECO.

Non-metallic tank, so no anode service.

Components & tests

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.

Diagnostic guides for this appliance

Guide · Water Heater

Heat-pump (hybrid) water heater: slow recovery, noise, errors

Hybrids need enough room air and a clean air filter, a working condensate drain and the right mode. Many complaints are mode settings or a dirty filter. Refrigerant faults are sealed-system work.

5 steps ~60 minmoderate

Guide · Water Heater

Tankless water heater descaling (flush)

Scale insulates the heat exchanger, causing overheat codes and fluctuating temperature. Flush with a pump and descaling solution through the isolation valves.

5 steps ~75 mineasy

Guide · Water Heater

Hot water recirculation pump problems

Check timer/settings, check valves, air in the loop and the pump itself. On tankless units with built-in pumps, a recirculation code may point to air or a leak in the loop.

5 steps ~60 minmoderate

Other water heaters manuals

Manual · Water Heater

Water heater brand families: A.O. Smith (State, American, Reliance, Lochinvar), Rheem (Ruud, Richmond, GE older), Bradford White (Jetglas) and store brands

US residential tank (gas and electric) water heaters under maker, sister and store brands, ~1998-2026; how to identify the builder from the rating plate.

2 components2 common failuresA.O. Smith, State, American, Reliance, U.S. Craftmaster, Lochinvar, Whirlpool, Kenmore, Rheem, Ruud, Richmond, GE, Bradford White, Jetglas

Manual · Water Heater

Rheem / Ruud / Richmond atmospheric gas tank with electronic thermopile control: quick sheet (diagnostic and electrical side)

Residential atmospheric-vent, standing-pilot gas tanks (Performance, Performance Plus, Professional Classic and the Ruud/Richmond equivalents, typically XG-prefix model numbers) built with the Guardian-style FVIR combustion chamber and a self-powered electronic gas control (White-Rodgers or Honeywell, depending on year). Power-vent and condensing Rheem tanks use different controls and are not covered here. Gas-side work (gas control, pilot, burner, thermopile replacement, venting) is diagnosis-and-refer only.

10 components8 common failuresRheem, Ruud, Richmond

Manual · Water Heater

A.O. Smith ProLine / Signature and State atmospheric gas tanks: quick sheet (diagnostic and electrical side)

Residential atmospheric-vent, standing-pilot FVIR gas tanks: A.O. Smith ProLine (plumber channel, e.g. GCR and GCG families), A.O. Smith Signature (sold at Lowe's) and comparable State models, with a thermopile-powered electronic gas control and status LED (Honeywell-type control on most current units). Power-vent, direct-vent and condensing models are excluded.

8 components7 common failuresA.O. Smith, State