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What You Need To Know About Tankless Water Heater Maintenance

Thinking about installing a tankless water heater? Maybe you recently installed one and are asking yourself, “Now what?” Here’s everything you need to know about tankless water heater maintenance.

Tankless water heaters are a fantastic option for almost any homeowner. They reduce energy consumption, lower your monthly water and water heating bills, and can have an incredible lifespan with proper maintenance. Tankless water heaters will last on average more than twice as long as tank water heaters, which means you can expect at least 10-15 years of life from your tankless water heater. That, combined with the monthly savings you’ll get, offsets the upfront cost and makes tankless water heaters a financially sound investment.

Here’s how to keep up with that preventative maintenance to extend the life of your tankless hot water heater: 

Start with Soft Water

Hard water is incredibly hard on a hot water heater. If you live in the Twin Cities region of Minnesota, the water entering your home primarily comes from (aquifers), a nearby lake, or the Mississippi River, all of which have naturally occurring sediments and mineral deposits (magnesium and calcium are the most common). The water entering your home has gone through an intensive filtration process to remove harmful contaminants. It makes it clean enough to drink, but the filtration doesn’t remove all of that sediment. That water can still have high levels of Total Dissolved Solids (TDS) in it, which can build up, clog pipes, and coat the interior of your water heater. In fact, traditional storage tank water heaters are under constant threat of reduced efficiency because of the sediment that can build up on the heating element or other parts of the tank. You’d be surprised at how thick the wall of crust inside a water heater can be just from residue left over from hard water. A tankless unit sidesteps many issues of a traditional tank system, but it’s still a good idea to start with soft water to keep your tankless system operating in the most energy-efficient way possible for as long as possible. 

TDS levels can be measured in grains per gallon, or parts per million. If you have a rating of over 10.5 grains per gallon (180 parts per million), that could be considered “Very hard”. You can check your local city’s water department page for a published TDS number, and you can also order water hardness test kits or purchase them at your local hardware store. If you decide to do an at-home test, make sure to test the cold water line that is entering your hot water heater; this will give you the most accurate reading. 

If your water test comes back on the “hard” or “very hard” end of the spectrum, you should consider installing a water softener system if you haven’t already. The water in your home would then go through an additional purification process that brings your TDS levels down, leaving less scale in the water to then buildup in your water heater or hot water valves and pipes. Installing a home water softener system can save you time and money: it’ll make your tankless water heater last long as well as your entire plumbing system, including faucets and showerheads. It can also reduce the yearly maintenance on your tankless hot water heater from 2 to 4 flushes to just 1. 

Perform Routine Maintenance

Plumbers aren’t the only people who should be performing routine maintenance on a water heater; homeowners can (and should!) build a maintenance schedule into their lives if they want their tankless system to continue to heat water effectively. Skipping the annual maintenance on your tankless water heater is the number one cause of a water heater failing before its advertised lifespan – and it can also void the warranty from the manufacturer. 

Here are the basic steps to performing an annual inspection on your tankless hot water heater (As always, consult your unit’s user manual or manufacturer’s website to get the most accurate information for your specific water heater): 

1. Check for error codes.

This will let you know if something happened to trigger an error code that you may not be aware of. You can consult your user manual to see what any error codes may mean, and call a water heater repair professional if anything seems too big to handle on your end. 

If there are no error codes, then you can move on to the next step.

2. Remove the front panel of the water heater.

Removing the front panel of your water heater is easy, but you must be careful to do it properly to avoid damaging the tabs holding it on. Consult your owner’s manual for specific instructions. 

3. Inspect the flame rod.

Without the front panel, you’ll be able to see what makes your water heater work. Find the flame burner to make sure that the flame rod is operating properly. You will notice a sight glass that allows you to peer through it to see tubes inside that are diffusing fire. What you want to see is a very clean blue flame coming out of the flame rod into the heat-exchanger area, where water is heated as it passes through. 

The whole heat-exchanger area is going to glow like a red flame, and this is exactly what you want. You also want to see a clean blue flame radiating underneath the heat-exchanger. This tells you that the gas pressure is proper and exactly how it should be. 

4. Remove and clean the air filter screen.

There will be a fresh air intake on your tankless water heater which prevents bugs and debris from getting in. Check the filter for anything that might be blocking the screen, and replace it with a new one if there is any damage to the filter itself. If there is an obstruction, your unit is not getting the proper air-gas mixture and will cause it not to work properly. 

5. Remove and clean the cold water filter & flush heater with vinegar‍.

Find the cold and hot domestic water supply valves and turn them off, isolating the unit so you can clean the cold water filter. Have a bucket ready to catch the water that will empty out of the unit – usually just a few quarts – when you remove the cold water valve cap. 

The cold water filter is located where the cold water intake pipe meets your water heater unit. Take it off and inspect it, then clean any debris or residue from the filter. You can use an old toothbrush to remove any buildup and rinse it under cold water. Then, reinsert the filter, making sure to feel the o-ring seat and ensuring the filter is finger-tight. Replace your cold water valve cap. Now you can turn the intake and outlet valve back on to flow water back into and out of your unit.

6. Flush your hot water heater with vinegar.

Connect service hoses to the hot and cold water lines. Shut off the hot and cold water valves to the heater, and turn on the valves to the service lines. Pour out the water from the heater into a 5-gallon bucket, and wait about 5 minutes for all the water to drain.

Next, pour 2-3 gallons of white vinegar into a 5-gallon pail that contains a sump pump. Connect the hose from the cold water inlet valve to the sump pump. Set the sump pump into the vinegar. Turn the hot and cold water valves on the service lines to the on position. Turn on the sump pump, and let the vinegar cycle through the heater, and let the vinegar drain back into the 5-gallon bucket. Cycle the vinegar through the system for about 30 minutes.

When finished, turn the cold water service valve off, and disconnect the hose. Turn the main cold water valve on. This will cycle clean water through the unit and rinse the pipes of any vinegar. Let the system cycle for about 5-10 minutes to ensure all vinegar is removed.

Turn the hot water service valve off, and remove the hose. Replace caps on both hot and cold service ports. Turn the hot and cold main water lines to the on position, then turn the water heater back on. Replace the front panel and your water heater is back in service. 

Pro Tip: Here’s a step-by-step guide with a video on how to perform an annual inspection on a Rinnai tankless water heater.

Keeping your tankless hot water heater clear of mineral buildup will keep your unit in the best shape possible. We recommend putting water heater maintenance on your calendar at least twice a year to ensure that it doesn’t fall off your radar. This will keep your hot water flowing and your energy bills as low as possible for the life of the unit. 

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