A water heater reset button, usually red, is located in the center of the limit switch just above the water heater thermostat.
The water heater limit switch is a safety device that will shut the power
down to the water heater if something malfunctions and the water gets to
hot. If this happens the limit switch can be reset by pushing the reset button in after the water cools down.
This is a pic. of a water heater thermostat, limit switch and reset button.
This thermostat is made for a duel element 240 volt storage water heater.
I have separated the thermostat and limit switch in this picture so you can see one from the other.
As you can see the limit and reset had been mounted on top of the thermostat.
The four terminals on this limit switch are numbered one through four.
Power enters the terminals 1&3 at the top and is transferred to terminals 2&4 on the bottom.
If the limit has tripped there will not be any power on terminals two and four.
You can check a water heater
limit switch a multimeter.
Turn the power off to the water heater. Set your multimeter to rx1. Put one probe on terminal 1 and one probe on terminal 2. On an analog meter the needle should sweep all the way over to zero. If it does the limit is not tripped.
If the limit is tripped follow the links below to find out why it had tripped. After you have made repairs or solved the problem push the reset button in to reset the limit switch.
Extremely hot water will cause a water heater limit switch to trip. If this
is the case you could have a grounded element. This will cause the
element to continue to heat. Water heater element testing.
You may need to test water heater thermostat to be sure its working properly.
If the element and thermostat check out ok the limit switch is
probably just weak. In this case replace the thermostat/limit switch.
electric water heater thermostat replacement