How To Flush Out A Tankless Water Heater

5 December 2018
 Categories: , Blog


Is your old water heater on its last legs and need to be replaced? If so, you may take this opportunity to switch to a tankless hot water heater instead of a traditional hot water tank. One thing to keep in mind is that this plumbing fixture requires different maintenance than traditional water heaters. Here is what you need to know about flushing out a tankless hot water heater.

Why Flush Out The Water Heater

You will need to flush out a tankless hot water tank annually in order to prevent buildup in the unit. While there is not a tank filled with water that needs to be drained, flushing out the tank will prevent lime scale from building up around the heat exchanger. Lime scale prevents the tank from heating up water as well as it can, which diminishes the unit's energy efficiency. The good news is that tankless models of hot water heaters will have minimal buildup when compared to a traditional hot water tank, but you still need to flush it out.

Shut Down The Water Heater

The first step you'll need to take is to properly shut down the tankless hot water heater. A gas model needs to have the gas line shut down by closing the valve going to the water heater. An electric model will involve unplugging the unit or shutting it down at the main circuit breaker.

Shutting off the water is necessary, and it helps to understand the valves leading to the water heater. If you had the tankless hot water heater professionally installed, there should be color coded valves. The blue valve controls the water entering the water heater, and the red valve is what controls the hot water that leaves the water heater. You'll need to shut off both valves.

Flush The Lines

The hot and cold water valves will have service ports where you can connect hoses to them. You'll want to connect a hose that goes from the cold water valve to a submersible pump in a bucket filled with white vinegar, and a hose from the hot water line that drains into your bucket. Run the pump for an hour to flush out the pipes of the water heater as it cycles through the pipes

When finished, disconnect the hose from the cold water line and turn the water back on. Let the water flow through the system and into the bucket for about a minute, which should clear out any white vinegar still in the system.