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 How to Test & Repair the Electric Water Heater High Temperature Cutoff & Reset Switch
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Fix the electric water heater reset switch: This article describes how and why to test the high temperature cutoff switch and how to use the hidden reset switch on electric water heaters.
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How To Test High Temperature Cutoff Switch Located at the Upper Heating Element
This series of articles describes how to inspect, operate, diagnose, and repair electric hot water heaters. The articles at this website will answer most questions about electrical water heaters
as well as many other building plumbing system inspection or defect topics.
Reproduction of this web page electronically at other websites is prohibited.
If you cannot find information you need here or if you have comments, questions, suggestions for inspecting and diagnosing water heaters Contact Us
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 Before testing the electric water heater elements we should check out the high temperature cutoff switch since a problem there will simply turn off power to both heating elements.
On an electric water heater the upper heating element may have two, three, or four electrical terminals, and above the upper thermostat is a high temperature cutoff switch with four terminals. You should be able to identify these parts by looking at the water heater's wiring diagram found on the tank or inside the panel cover.
The electric water heater high-temperature cutoff switch will turn off the entire water heater if temperatures are too high. If this cutoff is not working the water heater will simply not heat at all. You can use this switch to test to confirm that the incoming electrical power circuit is indeed bringing power to the water heater.
Turn off electrical power to the heater at the electrical panel: WARNING: possible fatal electrical shock. See Using DMMs & VOMs Safely and see VOLTAGE DETECTION & MEASUREMENT. General electrical inspection safety advice is at SAFETY for ELECTRICAL INSPECTORS.
Set the multi tester or VOM to its 250 VAC scale, and attach the tester probes or alligator clips to the two uppermost terminals on the control (L1 and L3 on the top left and top right in our photo below). These are normally the incoming electrical wires from the power circuit to the heater. "L" refers to "Line voltage" on most controls.
Test for line voltage: Now you can turn on electrical power to the heater. Your VOM should show voltage close to the voltage on the water heater's identification tag: typically this will be 208V or 240V for a 240V water heater, or it might be just 115V or 120V for a 120V water heater. If you do not see voltage close to the rated voltage you need to call an electrician to diagnose and repair the problem.
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Turn off Electrical Power to the Water Heater again. Don't skip this step or you may be killed or you may ruin your test equipment.
Test the High Temperature Cutoff Switch itself: set the VOM to its Ohm or resistance scale using the most sensitive setting (R x 1). Touch one probe to the upper left terminal on the control (L1 in our photo at left). Touch the other probe to the lower left hand terminal on the control (T2 in our photo at left).
The ohm meter needle should move (or your digital multimeter DMM should show some number other than infinity). If no continuity and infinite resistance is what you read, try pressing the reset button on this control (the red "RESET" button in our photo at left).
If you cannot reset the control then this device is not working and it needs to be replaced.
FYI we do not usually find a problem with this electric water heater high limit cutoff switch. The most common problem on an electric water heater that is not heating is a burned-up water heating element - tests that we describe next at How to Test Electric Water Heating Elements. |
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Frequently Asked Questions (FAQs) about how to test & repair or replace the electric water heater high temperature cutoff or reset safety switch
Question: my electric water heater is not working
no hot water. I have n electric hot water heater. - Paul 11/1/12
Reply:
Paul,
Check that the water heater has electrical power, then try pressing the reset switch described above.
Electric water heaters are among the easiest to troubleshoot;
There are just a few things to check, easily done with a digital multimeter (DMM)or volt ohmeter (VOM). Just go through the list starting with the links below at
Electric Water Heater Repair Guide (link shown below)
- check
- that water flows into and out of the heater
- for power to the heater
- that the thermostatic control is functional (article above)
- that the heating elements are not burned out
See ELECTRIC WATER HEATER REPAIR GUIDE for our complete & detailed electric water heater troubleshooting procedures.
Watch out: removing access covers on an electric water heater exposes live voltage-wires: touching them can cause injury, shock, or death.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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