How to Repair a Tankless Water Heater

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What You'll Need
Phillips head screwdriver
Element wrench
Hair dryer
Masking tape
Battery-powered volt meter

Occasionally you will need to repair a tankless water heater, replacing the heating element. Periodic maintenance will ensure more efficient operations. If you notice either a drop in water temperature or none whatsoever, then replacing the heating element will be a necessary repair. Here’s what you need to do.

Step 1 - Turn Off Power

Turn off the electrical power at the control panel or breaker box. Place a piece of masking tape over the switch so no one turns the power back on while you are replacing the heating element. Check the circuit with a volt meter even if the reading is “off” on the panel display. This will ensure you turned the correct breaker off. When working around electricity you always need to be sure because an error cannot only be dangerous, but can be deadly.

Step 2 - Open Hot Water Faucet

Open one hot water faucet while turning off the water supply to the heater. This will allow some water to siphon out of the heater.

Step 3 - Drain the Heater

Remove the six screws at the right bottom of the cleanout on the underside of the heating chamber plate with a Phillips head screwdriver, draining the rest of the water in the heater into a bucket. Once drained, replace the cleanout plate.

Step 4 - Remove Wires

Remove the screws that secure the red and black wires at the top of the heating element.

Step 5 - Remove Old Element

Loosen the heating element with an element or adjustable wrench. Make sure to wrap a rag around the heating element so no water will drip onto the control board. Disconnect the heating element along with the O-ring from the heater.

Step 6 - Seat New O-Ring

Check to see that the new O-ring seal is properly seated in the new heating element and install the assembly into the heater. Make sure to tighten the element snugly.

Step 7 - Replace Wires

Replace the red and black wires at the top of the element with two screws using a Phillips head screwdriver.

Step 8 - Turn on Water Supply

A tankless water heater.

Before turning on the water supply, makes sure the drain plug screw is tight. Always look for water around the heater element and drain plug.

Step 9 - Dry the Control Board

In the event that some water drips onto the control board, use a hair dryer to dry the control board making sure to dry behind it as well. Dry for a considerable time to make sure all water has evaporated. The control board cannot be harmed.

Step 10 - Fill Up and Heat

Fill the heater with water checking for any leaks. If none, turn the power switch on.


Once operating the heater again, if an alarm sounds displaying a 126 diagnostic code, moisture has been detected and the controls disabled. Check for leaks, and dry the entire heater thoroughly and then restart.