How to Flush the Heat Exchanger in a Rinnai Water Heater

Unplug the Rinnai water heater power cord from its dedicated outlet. Turn off both water supply valves below the unit.

Place a 5-gallon bucket on the floor near the water heater. Set a portable recirculating pump on the floor next to the bucket. The recirculating pump has two hoses attached to it, with the opposite ends of the hose having a connector like a garden hose.

Screw the pump outlet hose onto the cold water supply valve on the Rinnai water heater. Check the manual for your recirculating pump to ensure which hose is the outlet hose. It is the hose pointing to the flow of water. The pipes on the Rinnai water heater have service valve that look similar to shut-off valves.

Connect a separate garden hose to the hot water service valve, and place the opposite end in the bucket. Place the end of the inlet hose of your recirculating pump into the bucket.

Fill the bucket with 4 gallons of food-grade white vinegar. Open both service valves on the Rinnai water heater supply lines. Plug the recirculating pump power cord into the wall outlet. Allow the pump to run for 45 minutes. The pump draws the vinegar into the water heater to remove lime and scale, and the vinegar passes through the drain hose into the bucket.

Unplug the recirculating pump after 45 minutes. Pull the end of the drain hose out of the bucket and place it on a towel. Turn off the cold water service valve and turn on the cold water supply shut-off valve. Allow the cold water to fill the water heater for five minutes.

Turn off the hot water service valve and open the hot water shut-off valve. Remove the pump hoses from the water heater. Plug the Rinnai water heater power cord back into its dedicated outlet.