The lower thermostat on a water heater is a sensor that ensures the bulk of the water in the tank reaches the optimal warmth for your usage and safety. If the lower thermostat stops working, you could end up with chilly water next time you want to take a shower or bath.
Replacing the lower thermostat isn't difficult to do, but you first need to know for certain that the thermostat is the issue behind your water heating woes. If you're not sure, call in a water heating professional for plumbing assistance.
Step 1: Locate the Old Lower Thermostat
Turn off the power to your water heater using the circuit breaker or shut-off switch or by simply unplugging the unit.
Locate the lower access panel door, which will look like an upended rectangle near the bottom of your tank. Use the screwdriver to loosen the screw holding the panel in place then remove the panel and set aside with the screw.
You should now see a piece of foam that is partly attached to other insulation within the unit so it doesn't remove fully. The foam does have a door cut out that you can lift up to get the piece out of your way. Lift the bottom edge of that foam door until it extends up and over onto the unit's exterior wall. Secure the foam door in place with electrical tape.
Now you have to contend with the plastic cover over the thermostat. Insert the edge of your screwdriver into the notch at the top of the cover then press up firmly. The tab should pop and release the cover, which you can set aside for now.
Step 2: Remove the Old Thermostat and Install the New
Examine the wires attached to the lower thermostat and make a note of the orientation using pen and paper or a digital camera. Use your screwdriver to loosen each screw at a time then pull the wires free of the thermostat. Note that the wires will simply dangle inside the unit until you install the new thermostat. Press on each mounting bracket on the sides of the thermostat, pull out on the thermostat, then discard the old part.
Slide the new thermostat into place on the mounting brackets and press backwards to snap into place. Hook up the wires, one at a time, to the correct terminals. Tighten the screws to fasten the wires in place. Snap the plastic cover firmly back over the thermostat.
Remove the tape from the foam door then press the door back in place. Secure the access panel door with its mounting screw. Restore the power at the circuit breaker or shut-off valve, or plug the unit back in. Conduct a test run to see if the heating problem has corrected. If the water heater is still experiencing problems or if you need assistance, talk to a professional like those at Brother's Plumbing.