Marathon maintenance is dramatically simpler than mainstream tank water heater maintenance because the biggest maintenance task on a standard tank — anode rod inspection and replacement — doesn\'t exist on Marathon. The composite tank doesn\'t need anode protection. Skip every anode rod step you\'ve read about elsewhere.
Annual tasks
1. T&P valve test (recommended every 6 months)
- Lift the lever briefly
- Water should discharge through the tube
- Release; flow should stop completely
- Drips after test = failed valve, replace
- Position a bucket beneath the discharge tube during the test
2. Visual inspection
- All fittings — no drip or weep marks
- Electrical disconnect — no scorching or melted insulation
- Drain pan — dry and intact
- Composite outer jacket — no impact damage, cracks, or distortion
3. Verify thermostat setting
- Factory 120°F is the sweet spot
- Below 120°F increases Legionella risk
- Above 130°F increases scald risk and energy cost
Optional: annual tank flush
Standard tanks need annual flushing to remove sediment. Marathon\'s composite tank doesn\'t shed corrosion products like glass-lined steel does, so sediment buildup is reduced. However, incoming water still carries some sediment, and a periodic flush is still beneficial:
| Water hardness | Flush frequency |
|---|---|
| Soft (0-5 gpg) | Every 2-3 years |
| Moderate (5-10 gpg) | Every 1-2 years |
| Hard (10+ gpg) | Annually |
Marathon flush procedure
- Power off at the breaker; verify with voltage tester
- Close cold water inlet shutoff
- Open a hot tap upstairs to break vacuum
- Connect hose to drain valve; route to floor drain or outside
- Open drain valve; drain 3-5 gallons into bucket and observe
- Continue full drain if sediment present
- Flush with cold water — open inlet briefly, drain again, repeat until clear
- Close drain valve; refill tank fully (open hot tap until steady)
- Restore power once tank is confirmed full
Critical: never restore power with the tank empty — dry-fired elements burn out instantly.
Element resistance test (every 5-7 years)
Marathon\'s 6-year element warranty matches typical element lifespan. Test resistance at year 5-7 to identify degradation before failure:
- Power off at breaker; verify with voltage tester
- Open upper access cover
- Disconnect one lead from each element
- Multimeter on Ω; measure across element terminals
- 4500W element healthy: 10-16 Ω
- 5500W element healthy: 8-10 Ω
- OL (open) = element failed; replace
- See element test guide
Periodic ECO reset verification
The Emergency Cutoff (ECO) is the safety device that trips at ~180°F if the upper thermostat fails closed. Annual check:
- Locate red button on upper thermostat
- If button is popped (tripped), there\'s a real fault — diagnose before resetting
- If button is flush (not tripped), no action needed
- Don\'t press unless tripped — it\'s a one-way reset, not a periodic exercise
What Marathon doesn\'t need
| Standard tank task | Marathon equivalent |
|---|---|
| Anode rod inspection at year 4-5 | Not applicable — no anode rod |
| Anode rod replacement at year 7 | Not applicable |
| Switch from magnesium to aluminum-zinc anode for sulfur smell | Not applicable |
| Powered anode upgrade for very hard water | Not applicable |
Optional upgrade: replace plastic drain valve with brass
Marathon ships with a plastic drain valve that may seize after several years (same issue as other tank brands ship with). Optional first-flush upgrade:
- After first annual flush, drain tank completely
- Remove plastic drain valve
- Install ¾" brass full-port ball valve with Teflon tape
- Refill tank; restore power
$15-20 upgrade prevents stuck valve in future flushes. See drain valve page.
Bottom line
Marathon maintenance is genuinely simpler than mainstream tank maintenance. T&P test semi-annually. Optional flush based on water hardness. Element resistance test at year 5-7. Skip every anode-rod task you\'ve read about. The composite tank itself needs essentially no maintenance — it\'s structurally designed for set-and-forget operation.