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Thermo-King
Water Heater

Model # 5-40-20RT8-2 Official Thermo-King electric water heater

Here are the diagrams and repair parts for Official Thermo-King 5-40-20RT8-2 electric water heater, as well as links to manuals and error code tables, if available.

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  • In the search box below, enter all or part of the part number or the part’s name.

Not all parts are shown on the diagrams—those parts are labeled NI, for “not illustrated”.

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For DIY troubleshooting advice and repair guides, visit our repair help section.

Error Codes

Model diagram and schematic

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ALL PARTS
Showing 10 of 23 parts  |
Thermostat 9000510
#7

Round electric diagram

Thermostat

Part #9000510

Replaced by #9001954015

?
Manufacturer substitution
This part replaces 9000510. Substitute parts can look different from the original.
BEST SELLER
$28.09 | 
18% OFF Phone Price : $34.09
In Stock
Anode Rod 9000705
#2

Round electric diagram

Anode rod

Part #9000705

Replaced by #100300397

?
Manufacturer substitution
This part replaces 9000705. Substitute parts can look different from the original.
$55.38 | 
10% OFF Phone Price : $61.38
In Stock
Access Cover 9001764
#19

Round electric diagram

Access cover

Part #9001764

This item is not returnable
$5.99
In Stock
Access Bolt 9000928
#20

Round electric diagram

Access bolt

Part #9000928

This item is not returnable
$4.99
In Stock
Access 9000927
#21

Round electric diagram

Access

Part #9000927

This item is not returnable
$4.99
In Stock
Wheelers Water Heater Temperature And Pressure Relief Valve 9000728
#1

Round electric diagram

Wheelers water heater temperature and pressure relief valve

Part #9000728

Replaced by #100108455

?
Manufacturer substitution
This part replaces 9000728. Substitute parts can look different from the original.
$35.56
In Stock
Thermostat 9000507
#11

Round electric diagram

Thermostat

Part #9000507

Replaced by #9000507015

?
Manufacturer substitution
This part replaces 9000507. Substitute parts can look different from the original.
$32.20 | 
16% OFF Phone Price : $38.20
In Stock
Thermostat 9000509
#9A

Round electric diagram

Thermostat

Part #9000509

Replaced by #100108424

?
Manufacturer substitution
This part replaces 9000509. Substitute parts can look different from the original.
$30.00
In Stock
Drain 9000058
#13

Round electric diagram

Drain

Part #9000058

Replaced by #100108269

?
Manufacturer substitution
This part replaces 9000058. Substitute parts can look different from the original.
$18.57
In Stock
Gasket 9000926
#22

Round electric diagram

Gasket

Part #9000926

Replaced by #9004099215

?
Manufacturer substitution
This part replaces 9000926. Substitute parts can look different from the original.
$51.99
In Stock

Most common symptoms to help you fix your water heaters

Choose a symptom to see related water heater repairs.

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Why isn't my water heater heating my water?

Main causes: lack of power, no gas supply, thermostat limit switch tripped, bad element, bad thermostat, gas valve failu…

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Why isn't my water heater making the water hot enough?

Main causes: thermostats need adjustment, water heater capacity too low, bad heating element, thermostat failure, excess…

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Why is there water in my water heater's drain pan?

Main causes: loose water pipe fittings, leaky drain valve, bad temperature-pressure relief valve, leaky heating element,…

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Why does my hot water smell like rotten eggs?

Main causes: water supply needs chlorine treatment, anode rod too reactive…

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Why isn't my water heater making enough hot water?

Main causes: broken heating element, thermostat failure, excessive tank sediment, tank size too small, burner valve asse…

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Why is my water heater making the water too hot?

Main causes: thermostat temperature set too high, thermostats need adjustment, faulty thermostat, shorted heating elemen…

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Why is my water heater's pressure relief valve dripping water?

Main causes: faulty pressure relief valve, water is overheating…

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Repair guides for electric water heaters

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How to replace a water heater element

How to replace a water heater element

If your water heater runs out of hot water quickly and one of the two heating elements has failed, replace the element f…

Read more
Repair difficulty
Time required
 30 minutes or less
How to replace a water heater temperature and pressure (T&P) relief valve

How to replace a water heater temperature and pressure (T&P) relief valve

Replace a broken temperature/pressure (T&P) relief valve on an electric water heater using these instructions.…

Read more
Repair difficulty
Time required
 15 minutes or less
How to replace an electric water heater thermostat

How to replace an electric water heater thermostat

If the water temperature fluctuates or you don't get enough hot water, follow these instructions to replace your water h…

Read more
Repair difficulty
Time required
 30 minutes or less

Effective articles & videos to help repair your water heaters

Use the advice and tips in these articles and videos to get the most out of your water heater.

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Wiring schematic symbols explained video

Wiring schematic symbols explained video

Learn some of the most common symbols found in a wiring diagram and what they mean.…

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Using a wiring schematic to trace a current video

Using a wiring schematic to trace a current video

Find out what’s wrong with your appliance by following a circuit.…

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Easy DIY water heater repairs

Easy DIY water heater repairs

Read about some water heater repairs that you can easily do yourself.…

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