How to Repair a Tankless Water Heater

tankless hot water heater
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What Is a Tankless Water Heater?

A tankless, or on-demand, hot water heater is an economical choice for heating water for laundry, dish-washing or showering. These heaters do not store hot water, so you're not using energy to heat the water, just to have it standing in the tank. Instead, when a flow-activated switch comes on, the heat exchanger turns on and heats the water as you need it. Tankless water heaters come in point-of-use styles, like a coffee pot plumbed into the water system, or as whole-house units.

But, like other things in your home, they need to be maintained and, sometimes, you might need to troubleshoot and repair them. For most issues, this is an easy project that you can do yourself.

Here are some instructions when dealing with common tankless heater problems.

Basic Maintenance

According to HomeAdvisor, it can take up to 20 years for your tankless heater to pay for itself with energy bill savings. So, it’s an investment worth preventative care. With routine maintenance, you can avoid having to repair your water heater, and it will last much longer. The process is pretty simple, and you don't need a lot of special equipment. A quick flush every six months should do the trick.

Supplies Needed:

  • 5-gallon bucket
  • Sump pump/submersible pump
  • 2 gallons white vinegar
  • Hose
  • Pliers

How to:

  1. Turn off the water inlet and outlet valves on the water heater.
  2. Flip the circuit breaker to off or shut off the gas to the heater.
  1. Find the tab for the pressure-relief valve. Pull the tab.
  2. Pour the vinegar into the 5-gallon bucket.
  3. Place the submersible pump in the bottom of the bucket.
  4. Run a hose from the heater's inlet to the pump and connect them.
  5. Connect another hose to the pressure-relief valve and run it into the bucket.
  6. Pump the vinegar through the heater for 15 to 20 minutes. This will remove any scaling that builds up from the minerals in your water.
  1. Shut off the pump. Unscrew the inline filter housing. Remove and clean the screen filters and then replace them.
  2. Run the pump out of the bucket to empty the lines of vinegar.
  3. Run clean water through the heater for a few minutes, using the same pump arrangement as before.
  4. Turn the water and power back on.

Replace the Heating Element

Over time, the heating element may wear out. Replacing it is also easy enough to do yourself.

Supplies Needed:

  • Masking tape
  • Volt meter
  • Bucket
  • Screwdriver
  • Pliers
  • Rag or towel
  • Hair dryer (optional)

How to:

  1. Turn off the power at the control panel or breaker box.
    Safety Tip: Cover the circuit breaker or power switch with masking tape so others know not to turn it back on.
  2. Check the circuit with a volt meter to be sure the power is, indeed, turned off.
  3. Open one hot water tap to siphon out some of the water.
  4. Drain the hot water heater into a bucket. Check the manufacturer's instructions to find out how to do that for your model.
  5. Remove the wires at the top of the element with a screwdriver.
  6. Remove the old element, wrapping it in a rag or towel to prevent drips onto the control panel. You may need pliers for this step, depending on the design of your heater.
  7. Seat a new O-ring and then the new heating element. Tighten the new element completely.
  1. Replace the wires on top.
  2. Check to be sure that you have replaced the drain plug and that the cover is tight.
  3. Turn on the water.
  4. If necessary, use a hair dryer to dry any drips on the control panel.
  5. Fill the water heater and check for leaks.
  6. Turn the power back on.

Troubleshoot for Other Problems

No Hot Water

  • Check both the power source and water supply to be certain that both are connected and turned on.
  • Check to be sure that shut-off valves are open and that water flows at the minimum flow rate to activate the switch.

Water Is Too Hot or Not Hot Enough

  • Set the unit temperature to 120 to 125 degrees. This is the recommended temperature for safety. If you live with small children or others with sensitive skin, you may want to reduce the temperature.
  • Clean the filters and fixture aerators.
  • Reposition the temperature sensor so that it is firmly attached to the appropriate pipe.
  • Descale the heater and flush it according to the maintenance steps.