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Marathon water heater thermostats
Marathon Upper thermostat
Upper thermostat
Larger image
Marathon Lower thermostat
Lower thermostat
Larger image
Marathon is ordinary non-simultaneous residential water heater
30 amp breaker, 10 gauge wire, 4500 watt elements.
Same EF and efficiency as ordinary steel tank, nothing special except lifetime warranty, tank is made of polybutene instead of steel, will not rust, does not require anode rod, ... downside is elements can burn out frequently, elements cost a lot to replace and are not generic.
Thermostats are generic off-the-shelf, and are widely available.
Residential installation: limited lifetime warranty on tank and 6 year warranty on parts. Online registration required.
Commercial installation: 5 year tank, 1 year parts.
Resources:
2020 Spec sheet
2020 manual
Review Marathon water heater

Marathon Upper and lower thermostats are generic
Installing any ordinary thermostat will not void produce warranty
Resource
Marathon parts sheet/ pdf
melted plate on marathonThe marathon plate (sitting under thermostat and element) appears to be a heat barrier to protect polybutene tank from damage caused by short circuit (insulation failure).
Short circuits cause high heat that can melt the plate.

According to Rheem, if the plate is damaged or melted or missing, then the heater is irreparably damaged.
Why? The metallic plate is factory-connected to the element port, and is not detachable and not a replaceable part. And once the plate has dissolved around element, then the thermostats are free floating on a loose metal plate, and might not read correct temperature of water.

This is good example of expensive heater that seems to promise trouble-free life except has hidden risks for the customer from the use of non generic parts, like elements, and vacuum valve, etc ... and parts must be 'manufacturer authorized components.' or it voids warranty. Manual page 4
... even more ridiculous that a single thin metal plate can render entire water heater into the landfill ...because the simple metal plate has no replacement protocol and the poly resin tank is not recyclable.

Fritz B was covered by lifetime warranty because he was original owner, registered the product, and had proof of purchase. But he had to get the free replacement from same company he bought original unit from, and the warranty does not cover shipping or installation.
Warranty sheet

If tank is not covered by warranty, then have another plate made at local fabrication shop or sheet metal shop... or call Rheem for a big whiff of modern supply-n-demand bullroy.
Overheated wires on elements generally do not affect thermostat ... unless wire on thermostat melts, or thermostat malfunctions and melts wire.
The upper thermostat ECO reset button can trip if thermostat wires are loose and begin to arc, or if wire melts due to high heat, or if melted plate in upper compartment gets hot ... so yes, in that instance the ECO red reset button on upper thermostat can trip if there is nearby heat source like a short circuit.
The actual upper and lower thermostats would not trip OFF and need 'resetting' like the ECO unless thermostat was somehow damaged. The thermostats would just turn off momentarily until high heat event ended.
ECO is required on upper thermostat as first line of safety in event water inside tank overheats due to failed thermostat or cracked element keeps heating after thermostat turns off. Tank is required to have TP valve to release water during high pressure or high temperature events.

Mechanical bi-metal thermostats used on all types of electric heaters are designed to read tank temperature through a hole located on back of thermostat.
Thermostats must sit flat and tight against tank and be covered by insulation.
If insulation is missing, thermostat reads cool temps from room and overheats tank.
If thermostat is not sitting flat and tight against tank wall, then thermostat will not read correct temperature.

The upper thermostat has a second hole so the ECO (red reset button, energy cut off) can read tank temperature independently. The ECO on 90-150° thermostats will trip at 170°F.
The ECO on commercial thermostats 110-170°F will trip at 190°F.
Ordinary water heater thermostats are mechanical bi-metal switches (like the old timey HVAC thermostats, before all HVAC controls converted to electronics and became expensive)
Resources: Read about Rheem thermostats and ratings

Upper and lower thermostats
thermostat temperature range
Ordinary marathon upper and lower
thermostats/
Rated 150 ℉/ fits any Marathon 120-240 Volt water heater.
High Limit trips at 170°
Thermostat differential 17-27°F
All values +/- 5
Thermostats are interchangeable/
Each works with Marathon water heater
89T is discontinued/ replace with Apcom or Therm-o-disc
Buy: 90-150° F for residential tank:
Rheem UV11698
Rheem SP11698
Camco 08163
Aprom / 110-160°
Water heater thermostats at Amazon
Camco thermostats at Amazon
More thermostats
Marathon thermostats High temperature thermostats:
Rheem heavy-duty marathon is rated for 170 ℉/  
10 year tank warranty/ 5 year parts
Typical bath shower is 104-110°F

170-180° is for commercial sanitation/ solar collectors etc ... dangerous without tempering valve.
High Limit trips at 190°
Thermostat differential 17-27°F
All values +/- 5

Buy: Rheem Upper thermostat:
Rheem SP8293 / 170°
Camco 08304 / 180°

Buy: Rheem lower thermostat
Rheem SP8295 / 170°
Camco 08314 / 180°
Therm-o-disc thermostat protectors
Thermostat protectors fit any therm-o-disc thermostat
Plastic protectors snap onto thermo-disc thermostats ... and cover electric terminals on thermostat and element.
Does not fit Aprom type thermostat or older, discontinued 89T thermostats.

Purpose: When you adjust temperature, or push reset button, the breaker can be ON because the covers will protect you from electric shock.
Product manuals say protectors are required .... missing protector is a shock hazard, but does not cause heater to malfunction.
Buy:
SP310040 upper protector
SP310010 lower protector
Rheem marathon elementUpper element is fused to help prevent dry fire
Use 1-7/8 element wrench
1.5" UNF straight fine thread not 1" NPSM straight// 12-14 threads per inch vrs 11.5
Read parts .pdf before buying
Buy:
1-7/8" water heater element wrench
SP210197/ 3800 watt
SP210201/ 3000 watt
SP210198/ 3800 watt
SP213670/ 4500 watt
SP213480/ 3000 watt
SP213540/ 2000 watt
SP610130/ 3800 watt
SP213820/ 3800 watt
SP610140/ 5500 watt
SP610150/ 3000 watt
Resource
Marathon parts sheet/ pdf
Regular water heater elements/ identify and replace
All brands of thermostats are interchangeable

$48
for 2 low density 240 Volt 4500 watt elements/  + Upper and lower thermostat


Buy:LOW density kit:
Apcom plumbers pack Amazon

Resource
How to replace elements
How to replace thermostats

$35 for 2 high density 240 volt 4500 watt elements + Upper and lower thermostat

Apcom thermostats
Buy: HIGH density kit:
Apcom plumbers pack Amazon

Resource
How to replace elements
How to replace thermostats

New water heaters have high density elements. Low density elements might last longer
$45 for 2 low density 240 Volt 4500 watt elements/+ Upper and lower thermostat

Therm-o-disc thermostats
Buy: LOW density kit:
Therm-O-disc low density plumbers pack

Resource
How to replace elements
How to replace thermostats
$45 for 2 high density 240 Volt 4500 watt elements/ + Upper and lower thermostat

Therm-o-disc thermostats
Buy: HIGH density kit:
Therm-O-disc high density plumbers pack
Therm-O-disc high density

Resource
How to replace elements
How to replace thermostats
water heater thermostat Take photo of wires ... before starting
Take photo of wires or draw picture showing location of each wire
Replace water heater thermostat
Larger image
See large image of overall wiring diagram
Wire colors can vary
Take photo of wiring before starting.

Steps to replace thermostat
Instructions are same for both upper and lower thermostats
Power is OFF, and tested that power is off using steps above

Remove wires from thermostat
Thermostat is held in place by metal spring that snaps over ears on thermostat
Pull back metal spring on both sides (make a tool using piece of coat hanger wire)
Slide out old thermostat
Put new thermostat in place, wiggle thermostat around to make sure it is held flat and tight against tank by metal spring
Thermostat reads temperature through surface of metal tank
Use screwdriver to adjust temperature
See images showing how to adjust temperature to 120 (or higher if hot water runs short)
Re-connect wires <> tighten screws very firm against copper wire
Important .... Push-in red reset button firmly to make sure it is engaged
After thermostat is replaced, put factory insulation back over thermostat
Insulation must cover thermostat to avoid higher water temperatures than desired set point
Tank must be full of water or elements will instantly burn out
Turn power ON
Put ear against water heater to hear bubbly fizzing sound that says water heater is 'on'
If tank is fully heated, water heater will not turn on. If tank is partially heated, then lower element will turn on. If tank is cold, then upper element will turn on. How it works
Put access doors back on tank
Access doors and insulation are required for thermostat to read correct temperature

Resources:
More detailed steps How to replace thermostats
If water heater is still not working, see troubleshooting
Use push-on wire connectors when wires are too short
Or use twist on wire connector.
Use ONLY solid copper wire ... NO stranded wire
Buy:
Push on wire connectors at Amazon
Red 3P connector (shown) for 10-14 gauge wire
Yellow 4P for 12-18 gauge wire
Push on wire connectors
Insulation and cover must be over thermostat
Exposing thermostat to cool room temperature will cause tank to overheat.
Thermostat cannot read correct temperature unless covered correctly.

Buy:
Upper element terminal protector
Lower element terminal protector
Resources:
Troubleshoot electric water heater
Water heater leak Inspection finds leak/ rust around element
Marathon shown on right: Leaking element on marathon will have little effect on brass threads where elements screw in, and leak will not cause rusted tank, because Marathon is Polybutene, not steel.

Steel tank shown on left: Leaking thermostat will damage ordinary steel tank, causing rust, possible short circuit.
Long term leak can rust the threads so element will never seal and heater must be replaced.

Resources
Replace element and gasket
Inspect anode rod
Leaking water heater resources
How to install electric water heater
Water heater must be full of water or elements instantly burn out.
How to fill water heater:
Turn tub spout ON until full stream.
Open water heater TP valve for a moment to release last of air.
Turn power ON.
Resources:
How to test elements
How to replace elements
How electric water heater works
How to test and replace TP valve
Support the economy:
Buy: water heaters from my associate links:
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40 gallon electric water heaters at Amazon
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How to install electric water heater
Troubleshoot gas water heater
Troubleshoot electric water heater
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Resources:
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