Element testing is the first diagnostic step on any Marathon "no hot water" or "lukewarm" complaint. A 5-minute multimeter test identifies which element (if any) has failed before you order parts.
What you need
- Multimeter with Ω (resistance) function
- Phillips screwdriver
- Voltage tester (verify power is OFF)
Procedure
- Turn off power at the 240V breaker. Verify with voltage tester at the element terminals
- Remove the upper access cover (Phillips screws)
- Fold back insulation and remove the plastic safety cover
- Disconnect one lead from the element (isolates the element from the circuit)
- Set multimeter to Ω — 200Ω range or auto-range
- Touch probes to the two element screws
- Read resistance and compare to spec
- Repeat for the lower element (open lower access cover)
Expected resistance values
| Marathon line | Element wattage | Healthy resistance | Acceptable range |
|---|---|---|---|
| Standard (MR series) | 4500W | ~13 Ω | 10-16 Ω |
| Heavy Duty (MHD series) | 5500W | ~9 Ω | 8-10 Ω |
| Lowboy (MRH series) | 4500W | ~13 Ω | 10-16 Ω |
Interpreting the reading
- OL (open) or infinite resistance: element burned out. Replace
- Near 0 Ω: element shorted internally. Replace
- Out of spec by more than 20%: element degraded. Will eventually fail. Plan replacement
- Within spec: element healthy. Issue is elsewhere (thermostat, ECO, breaker)
Element-to-ground short test (critical)
With multimeter still on Ω, touch one probe to an element terminal and the other to the tank shell or ground bolt. Should read OL (open).
- OL = good. Element is not shorted to ground
- Continuity (any reading) = element shorted to sheath. Replace immediately. Don\'t restore power until replaced — shorted element trips breakers and can damage the contactor
Common failure patterns
- Lukewarm water, slow recovery: lower element failed. Upper continues heating the top portion
- No hot water at all: upper element failed (upper is the primary)
- Breaker trips on reset: element shorted to ground. Confirmed by ground test above
- Element appears OK but no heat: check thermostat continuity before condemning element
Replacement procedure
If element is bad:
- Drain tank to below the failed element (lower element = full drain; upper = drain ~½ tank)
- Disconnect both leads from the element
- Use 1-1/16" element wrench to unscrew (Marathon uses standard ¾" element threads)
- Install new element with new gasket
- Refill tank — open hot tap until steady stream (verify no air pockets)
- Restore power only after tank is confirmed full (never dry-fire)
Element compatibility
Marathon uses industry-standard ¾" screw-in elements. Universal 4500W and 5500W elements interchange with Marathon. OEM Marathon elements are slightly more expensive but offer the same construction. Generic Camco, Rheem, or AO Smith elements at correct wattage fit and function identically.
Bottom line
Element ohm test is the cheapest, fastest Marathon diagnostic. Always test before ordering parts. Element-to-ground short test catches dangerous conditions. Within 6-year parts warranty, Marathon ships replacement free — homeowner pays labor.