How to Flush a Tankless Water Heater: A Step-by-Step Guide

Did you know that the lifespan of your tankless water heater can be significantly shortened if you neglect proper maintenance? Scale buildup from hard water can wreak havoc on its internal components, leading to reduced efficiency, lukewarm showers, and eventually, costly repairs or replacements. Flushing your tankless water heater annually is a simple yet crucial task that removes these mineral deposits, ensuring optimal performance, energy savings, and a longer lifespan for your investment. Ignoring this maintenance can be a very costly mistake.

Tankless water heaters provide on-demand hot water, saving energy and space compared to traditional tank-style heaters. However, they require regular flushing to maintain their efficiency and prevent damage. This process removes mineral buildup that accumulates over time, particularly in areas with hard water. By flushing your tankless water heater, you can prevent costly repairs, extend its lifespan, and ensure you always have a reliable source of hot water when you need it.

What are the steps to properly flush my tankless water heater?

Why do I need to flush my tankless water heater?

You need to flush your tankless water heater to remove mineral buildup, primarily calcium and magnesium, that accumulates over time from hard water. This buildup, known as scale, reduces the heater’s efficiency, restricts water flow, can cause overheating and damage to components, and ultimately shortens the lifespan of the unit.

Scale acts as an insulator, forcing the tankless water heater to work harder and longer to heat water. This increased workload translates to higher energy bills and potentially premature failure of the heating element or other critical parts. Reduced water flow can manifest as weak hot water pressure or inconsistent temperature delivery. Furthermore, overheating can trigger safety shut-offs, leaving you without hot water. Regular flushing dissolves and removes these mineral deposits, restoring optimal performance and preventing costly repairs. The frequency of flushing depends on the hardness of your water. If you have very hard water, you might need to flush your tankless water heater every six months. In areas with softer water, flushing every year or two might suffice. Consulting your water hardness report and the manufacturer’s recommendations for your specific unit is the best way to determine the appropriate flushing schedule. Ignoring the need for flushing leads to a gradual decline in performance and an increased risk of significant damage, negating the long-term cost savings a tankless water heater is designed to provide.

What supplies are needed to flush a tankless water heater?

To properly flush a tankless water heater, you’ll need a few key supplies: a submersible utility pump, two lengths of washing machine hoses, approximately two to five gallons of white vinegar, a five-gallon bucket, and possibly a pipe wrench or adjustable wrench for hose connections.

While the submersible pump is the workhorse of the flushing operation, circulating the cleaning solution, the other items are equally vital. The washing machine hoses create a closed loop between the bucket, the pump, and the water heater, allowing the vinegar to flow through the system. White vinegar is the recommended cleaning agent because it’s a mild acid that effectively dissolves mineral buildup without damaging the internal components of the tankless water heater. The five-gallon bucket serves as the reservoir for the vinegar solution and to collect the flushed water. Depending on the type of connections on your water heater’s service valves, you might need a pipe wrench or adjustable wrench to securely attach the washing machine hoses. Ensure all connections are tight to prevent leaks during the flushing process. Some kits are available that contain all these supplies, which can be a convenient option.

How often should I flush my tankless water heater?

You should flush your tankless water heater at least once a year, and ideally twice a year, especially if you have hard water. This regular maintenance removes mineral buildup that can significantly reduce efficiency, shorten the lifespan of your unit, and even void the warranty.

The frequency of flushing depends heavily on the hardness of your water supply. Hard water contains high concentrations of minerals like calcium and magnesium. As water is heated, these minerals precipitate out of solution and form scale inside the heat exchanger of your tankless water heater. Over time, this scale acts as an insulator, making it harder for the unit to heat water and forcing it to work harder, thus consuming more energy. If you know you have hard water, you might consider flushing every six months. Regular flushing not only improves the efficiency of your tankless water heater but also prolongs its lifespan. A buildup of scale can lead to overheating, component failure, and eventually, a complete breakdown of the system. Neglecting this routine maintenance can lead to costly repairs or the need for a premature replacement. Furthermore, many tankless water heater manufacturers require regular flushing as part of their warranty terms. Failure to comply with these requirements can void your warranty, leaving you responsible for all repair or replacement costs.

Can I damage my tankless water heater by flushing it incorrectly?

Yes, you can absolutely damage your tankless water heater by flushing it incorrectly. Improper flushing techniques or using the wrong solutions can lead to scale buildup, corrosion, and damage to sensitive components like the heat exchanger, potentially shortening the lifespan of your unit or requiring costly repairs.

Flushing a tankless water heater involves circulating a descaling solution through the unit to remove mineral buildup, primarily calcium and magnesium, which accumulate over time from hard water. Using harsh chemicals like muriatic acid (hydrochloric acid) instead of a specifically formulated descaling solution is a common mistake. Muriatic acid is far too aggressive and can corrode the heat exchanger and other internal parts, leading to leaks and premature failure. Similarly, using excessively high pressure during the flushing process can damage seals and connections. Another potential issue arises from incomplete flushing. If you don’t adequately rinse the descaling solution from the system after the process, residue can remain and continue to react with the metal components, causing ongoing corrosion. Always follow the manufacturer’s instructions carefully, paying close attention to the recommended descaling solution, flushing time, and rinsing procedure. Failure to properly isolate the unit from the main water lines or not fully closing valves can also introduce contaminants or cause pressure imbalances that can harm the heater.

What kind of solution should I use when flushing my tankless water heater?

The best solution for flushing a tankless water heater is a mixture of white vinegar and water, typically in a 50/50 ratio. This solution effectively dissolves mineral buildup, such as calcium and lime scale, that accumulates over time and reduces the unit’s efficiency. Never use harsh chemicals like bleach or muriatic acid, as these can damage the internal components of the water heater.

When selecting a flushing solution, prioritize safety and compatibility with your tankless water heater. White vinegar is a mild acid that’s safe for most metal components found in these systems, including copper and stainless steel. The dilution with water further reduces its aggressiveness while still maintaining its cleaning power. Using stronger acids or chemicals not specifically designed for tankless water heaters can corrode pipes, damage heat exchangers, and void warranties. Always consult your tankless water heater’s owner’s manual for specific recommendations regarding flushing solutions. Some manufacturers may suggest using a commercially available descaling solution specifically formulated for tankless water heaters. These solutions often contain a blend of acids and inhibitors that are designed to remove mineral deposits without harming the unit’s internal components. Regardless of the solution you choose, always follow the manufacturer’s instructions carefully for dilution ratios and flushing procedures. Ignoring these guidelines could lead to damage or ineffective cleaning.

How do I know when the flushing process is complete?

The flushing process is complete when the water running clear through the drain hose indicates that all sediment and mineral deposits have been removed from the tankless water heater. There should be no more discoloration, cloudiness, or particulate matter visible in the outflowing water.

The clearest indication that the flushing is complete is visual. Initially, you’ll likely see murky or discolored water exiting the drain hose, possibly containing small particles. This is the accumulated scale and sediment being dislodged from the heat exchanger. Continue circulating the flushing solution (usually vinegar or a commercial descaler) until the water begins to run clear. Periodically check the outflow; if you notice a significant reduction in debris and the water appears clean and transparent, it’s a good sign you’re nearing completion. Beyond visual confirmation, you can also check the pH level of the outflowing water if you used a descaling solution. If the pH is nearing the pH of the water you are using to rinse, this can be another indication that the system is clean. Don’t rely solely on pH, however; the visual cue of clear, sediment-free water is the most reliable indicator. Remember to rinse thoroughly with clean water after using any descaling solution to remove any residual chemicals. The rinsing is also complete when the outflow is clear.

Where are the service valves located on my tankless water heater?

Service valves on a tankless water heater are typically located on the cold water inlet and hot water outlet pipes, directly beneath the unit. They are usually color-coded, with the cold water valve often being blue and the hot water valve being red.

These valves are specifically designed for isolating the water heater from your home’s plumbing system, making it easier to perform maintenance tasks like flushing. The service valves allow you to shut off the water supply to the heater without having to shut off the water to your entire house. Some models may also include a third valve connecting the two service valves with a short section of pipe to attach a pump and bucket for descaling.

If you’re having trouble locating the service valves, consult your tankless water heater’s user manual. The manual will provide specific diagrams and instructions for your model, which can vary slightly depending on the manufacturer. If your water heater was installed without service valves, you will need to install them prior to performing a flush. A plumber can add them if you are uncomfortable with plumbing.

And that’s all there is to it! Flushing your tankless water heater might seem a little daunting at first, but with these steps, you can keep it running smoothly and efficiently for years to come. Thanks for reading, and we hope this guide helped you out. Feel free to swing by again for more helpful tips and tricks around the house!