Things You'll Need
Electric hot water heater thermostat (upper and lower, if necessary)
How to Replace an Electric Water Heater Thermostat. You step into the shower and turn on the hot water faucet, all set for a nice, hot shower. Instead you get only cold water. You may need to repair your electric hot water heater. If the water isn't heating up, the culprit could also be the thermostat. Replacing the thermostat on your electric hot water heater can have you singing in the shower again in no time.
Remove the access panel, and check both thermostats on the water heater. An electric hot water heater has an upper and lower thermostat to control the upper and lower heating elements. Test both thermostats; you may need to replace one or both.
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Turn off the electrical power to the water heater at the circuit panel. Disconnect the wires from the terminals on the thermostat.
Unscrew the thermostat from its mounting, and remove. Replace thermostat with one of the same size and model you can purchase from any home improvement store or electrical supply outlet. Screw onto mounting, and connect wires to the terminals.
Repeat the process, if you are plan to replace both the upper and lower thermostats. In both cases, push the thermostat firmly back against the tank to ensure it works properly.
Attach access panel to the water heater. Turn power back on at the circuit panel. Adjust the thermostats following manufacturer instructions in the owner's manual for the electric hot water heater. Test to make sure the water heater is now working properly.
Check the limit switch present for the top thermostat. If the water gets too hot, this switch trips and turns off power to both the upper and lower heating elements. Press the red button on the switch to reset, and see if this resolves the problem before replacing the thermostat.
Always consult with a licensed electrician if unsure about making electrical connections.