How to Flush a Rinnai Tankless Water Heater? – 6 Steps

Learning and mastering how to flush a Rinnai tankless water heater is the responsibility of every homeowner who owns such water heating systems.

Flushing is vital to keep the Rinnai tankless heater functioning optimally, especially if you use well water or other sources with high concentrations of minerals and particulates.

The good news is that flushing a Rinnai tankless water heater is straightforward, and we will show you how.

Step-by-Step to Flush a Rinnai Tankless Water Heater

What to prepare

We recommend a tankless water heater flushing kit to avoid guessing what materials and tools to prepare.

Step 1. Disconnect the Rinnai tankless water heater from its power source.

To start the tankless Rinnai flush procedure, you need to cut off the electricity or gas supply power to the water heater.

To do so, go to your house’s electrical panel, open it, and look for the circuit breaker connecting the grid to the tankless water heater. Turn the switch into the “off” position.

For gas-powered Rinnai tankless water heaters, look for the gas supply shut-off valve along the pipe running to your water heater and cut it off.

Step 2. Close the Rinnai tankless water heater valves

Your Rinnai tankless water heater has two colored valves: blue, which is the inlet for cold water, and red, which is the inlet for hot water. You might also see a third valve supplying water to the rest of the home.

You might want to check your owner’s manual or the Rinnai tankless water heater troubleshooting guide for these valves’ precise locations on your unit.

Turn the valve handle perpendicularly, forming a letter “T” relative to the water pipe. This action “closes” the hot and cold water valves.

You will also notice a rubber-sealed purge port valve on the hot and cold water valves. Carefully remove the caps on the purge valves.

Step 3. Connect purging hoses to the tankless water heater purge valves or service valves and the circulation pump.

Insert hoses to the Rinnai tankless water heater purge valves, both hot and cold. Check that the hosing lines can bridge the tankless water heater to the bucket on the floor. Then, make sure the connection is water-tight to avoid leaking or flooding.

Connect the cold water (inlet valve) hose’s open end to the discharge port of the circulation pump. Meanwhile, place the hot water (outlet valve) hose’s other end to the bucket.

Then, place the open-ended hose of the circulation pump into the bucket to complete the water circuit.

Step 4. Flush the Rinnai tankless water heater.

It’s best to flush the Rinnai tankless water heater with vinegar. To be clear, not any vinegar will do; only white, undiluted, and food-grade vinegar should be used to descale Rinnai tankless water heater units.

In any case, avoid chemical cleaning agents, as they might stick to the tankless water heater pipes and impact your family’s health.

Pour the white vinegar into the bucket and turn the hot and cold purge valves perpendicularly to the hot and cold water valves. This action opens the purge valves and facilitates flushing.

Turn on the circulation pump and leave the setup for at least 45 minutes. Let the pump do its job for 1–2 hours for better results if possible.

Step 5. Flush or rinse the tankless water heater to remove cleaning agent residue.

Switch off the circulation pump. Then, close the purge valves by turning them parallel to the hot and cold water halves. Remove the hosing line connected to the inlet valve for cold water, but keep the outlet for the hot water hose linked.

Open the inlet valve for cold water by twisting the handle parallel to the water pipe. This action allows cold water to move along the tankless water heater’s heat exchanger pipes.

Leave the cold water running through the system for about five to ten minutes to remove as many cleaning agent residues as possible. Assess the water from the hot water valve hose for any scent of vinegar.

Step 6. Finish up.

Close the cold water valve once you are satisfied with the flushing.

Next, turn off the hot water purge valve and disconnect the hose. Replace the purge valve port caps and open the cold and hot water valves.

Reestablish power to the Rinnai tankless water heater by switching on the correct circuit breaker at the electrical panel (for electric units) or turning on the gas supply shutoff valve.

Open a hot water faucet to purge air trapped in the plumbing system. There should be a steady, sputter-free water flow coming out.

Frequently Asked Questions

Can I flush my tankless water heater myself?

Yes, you can flush a tankless water heater yourself as part of routine maintenance.

However, you need confidence, sufficient knowledge of tankless water heater systems, and the correct tools to flush the unit.

You can buy a tankless water heater flush kit to avoid guessing what materials and tools to prepare. These products comprise hoses, cleaning agents, a recirculating pump, and a collecting bucket.

As always, you will be better off with a professional if you are clueless about what to do.

How often to flush a Rinnai tankless water heater?

The frequency of flushing Rinnai tankless water heater units depends on water quality and consumption. Rinnai’s heat exchanger requires periodic flushing to prevent limescale-related damage.

The good news is that servicing Rinnai tankless water heater units is more straightforward than other brands. These tankless water heaters have a digital screen that displays an “Error Code 55,” indicating it’s time to flush and service the unit.

If your Rinnai tankless water heater doesn’t have a digital display, then you’ll need to flush the system yearly to remove mineral deposits in the heat exchanger.

How much does it cost to flush a Rinnai tankless water heater?

On average, professional plumbers charge about $150 for a tankless water heater flush cost for homeowners who cannot clean Rinnai tankless water heater units themselves.

Some plumbers might charge up to $250 per water heater flush. Although it might seem inflated, this price is still lower than replacing the tankless water heater due to limescale-related damage.

How long does it take to flush Rinnai?

How long to flush tankless water heater units from Rinnai depends on who’s flushing and the water quality (i.e., sediment-loaded well water). In general, flushing a Rinnai tankless water heater takes at least 45 minutes.

Conclusion

How to flush a Rinnai tankless water heater is a straightforward process requiring closing valves, connecting the hose and the heater and a circulating pump, and then opening the service valves.

It is a 45-minute wait, enough time to check your Rinnai tankless water heater for other issues. After all, flushing is only one of the essential activities for maintaining and caring for your water heater.

Hopefully, this how-to guide made you more confident in flushing a Rinnai tankless water heater

Read next: How Frequently Should You Flush a Water Heater?