Will hard water hurt a tankless water heater?

Author: Grant Murray  |  Last update: Friday, March 27, 2026

When hard water is heated, the minerals can precipitate out of the water and form scale deposits inside the heater's heat exchanger and other components. This buildup can reduce the heater's efficiency, impede water flow, and lead to costly repairs or premature failure.

How do you maintain a tankless water heater with hard water?

Flush to remove hard water deposits

Your tankless water heater should be flushed at least annually. This is to remove mineral deposits, such as calcium. If you've had hard water problems in your home, you might consider flushing out your heater more than once per year to counter mineral deposits.

Do I need soft water for a tankless water heater?

A water softener is essential for the efficient operation of your tankless water heater. By removing the hardness minerals before they can clump together and form scale, a water softener ensures that your heater runs smoothly and maintains its efficiency.

What do plumbers think of tankless water heaters?

St Paul Pipeworks plumbers advise against purchasing tankless water heaters from big box stores or online retailers, as homeowners often lack the expertise to determine the correct sizing for their specific needs. Many negative reviews about tankless systems stem from improper sizing or piping installations.

Can you take a long shower with a tankless water heater?

If you're in a warmer climate and have low-flow shower heads that use 1-2GPM, you might be fine with a 6GPM tankless system and 2 people taking a shower and someone using a sink... but if you're in a colder climate it might not be good enough for a shower + sink.

Unbelievable Hack: Instantly Fix Your Tankless Water Heater Without Any Error Codes!

What is the downside of a tankless water heater?

Before you commit to buying a tankless water heater, the primary drawbacks to know include: Higher upfront costs. Tankless water heaters are, on average, quite a bit more expensive to buy and install than tank water heaters. Access to fuel.

Why does my shower go cold after a few minutes tankless water heater?

One possible reason for a tankless water heater going cold after a few minutes is the occurrence of a cold water sandwich effect. This happens when the unit is turned on and the initial cold water mixes with the hot water, resulting in an inconsistent flow of hot water.

What is the lifespan of a tankless water heater?

Tankless water heaters usually last for around 15-20 years before they need to be replaced, but they may need replacing sooner if they start to break down or lose efficiency. Some common signs your tankless water heater needs to be replaced include: Low water pressure. Water doesn't get hot.

Why don't more people use tankless water heaters?

Some people hesitate to decide on a tankless water heater because they can be a slightly higher cost; however, you get significantly more life out of one. A standard water heater tank lasts about 8-12 years. A tankless water heater can last as long as 25 years!

Do tankless water heaters increase water bill?

Because tankless water heaters only consume energy when you need hot water, they're more energy efficient, saving you money on water and energy bills.

Will hard water ruin a tankless water heater?

Yes, but not as well as they should and hard water voids the manufacturers warranty. Hard water is a common problem that can lead to clogs and other issues in your tankless water heater.

How to protect a tankless water heater from hard water?

Here's how you can help mitigate the issue:
  1. Install a Water Softener: This is one of the most effective ways to prevent sediment buildup. ...
  2. Regular Descaling: If a water softener isn't an option, regular descaling can help.

When not to get a tankless water heater?

Electric Tankless Water Heaters

They're less expensive than gas-powered ones but aren't efficient if you run multiple hot water devices. They may struggle to keep up with multiple appliances at the same time.

Does hard water damage water heater?

You see, hard water contains several minerals, mostly calcium and magnesium. While these minerals probably won't threaten your health, they can surely hinder the performance of your water heater and significantly reduce its lifespan. Your pipes and plumbing system can also suffer the same fate.

Why does hot water run out quick when you have a tankless water heater?

Although your tankless unit is designed to provide hot water on demand, it has a specific capacity. You can potentially exceed this capacity by running too many faucets or showers at one time. As a result, you can end up with a cold shower.

How do you soften permanent hard water?

Temporary hardness can be removed by boiling, but permanent hardness cannot be removed with this method. Water softening at home can be done using a resin coated with sodium. Other methods of removing hardness include Clark's process, Calgon's process, and ion-exchange resin.

What is the downfall to a tankless water heater?

A tankless water heater cannot provide hot water faster than its ability to heat the water. While a tank unit can provide hot water for multiple uses at once, a tankless unit might not be able to support simultaneous usage, such as washing dishes, taking a shower and running a washing machine all at once.

Can I replace my 40 gallon water heater with a tankless water heater?

Absolutely! In fact, tankless water heaters are becoming the standard for new home construction because of the energy efficiency.

How long can a tankless water heater run continuously?

Total run time can range from one to two hours for new tankless water heaters to five or more hours for older tank style water heaters.

Do tankless water heaters need to be flushed every year?

Over time, a tankless water heater may accumulate mineral build up which can erode the walls inside your tank's heating chamber. To properly maintain and clean your tankless water heater, it's important to flush those mineral deposits at least once a year.

What is one disadvantage of a whole house tankless water heater?

More expensive installation and maintenance.

Tankless systems require special venting, rerouted gas lines, possibly multiple units for a larger household, and sometimes maintenance like installing a softener.

How long do water heaters last with hard water?

How long will a water heater last with hard water? While actual life expectancy varies based on the water heater, hardness of the water, and maintenance schedule, hard water will likely reduce the life expectancy of the water heater by about two years.

What maintenance does a tankless water heater need?

The most complicated and time-consuming tankless water heater maintenance is typically descaling and flushing out the unit. Even with the inline water filter, lime and calcium deposits can build up inside the tankless system. If you have hard water, it's a good idea to descale and flush the unit once a year.

Why does my tankless water heater stop heating during shower?

A tankless water heater requires a certain amount of water pressure to function properly. If the incoming water pressure is too low, the unit will not be able to generate enough hot water.

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