Top 8 Ways Tankless Water Heaters Are Installed Incorrectly

A tankless water heater is an investment for your home that can give you endless hot water. When correctly installed, tankless water heaters can work for 20+ years. But how can you know if your plumber or contractor correctly installed it?

We don’t mean to alarm you, but if they’re not certified by the water heater’s manufacturer, you just have to take them at their word, until now.

At Monkey Wrench Plumbing, Heating, Air & Electric, we’ve worked all over the greater LA area, and we’ve seen some crazy tankless water heater installations. So, we’ve created this article to help you find out if your tankless water heater is installed correctly.

By the end of this article, you will learn the eight common tankless water heater installation mistakes, why they’re a problem, and how to spot them. We’ll also give you the next steps to take if you discover your tankless water heater is incorrectly installed.

1. Using an Outdoor Model Indoors

When installing a tankless water heater, the first big mistake someone can make is using an outdoor model indoors.

Why Is This a Problem?

Using an outdoor tankless water heater inside your home can be life-threatening because the fumes from the exhaust will fill the room. This oversight is extremely dangerous because it can cause carbon monoxide poisoning.

An indoor tankless water heater from Noritz. The vent pipes are located above the Monkey Wrench Plumbing, Heating, Air & Electric Sticker.

So, how can you tell if your tankless water heater is an outdoor model? Here are four easy ways to tell:

• The model has outdoor (OD) written on it.
• There is no venting coming out of the top of the water heater.
• There are vent slits on the face of the water heater.
• Your carbon monoxide sensors are going off.

An outdoor tankless water heater by Noritz has a vent under the Monkey Wrench Plumbing, Heating, Air & Electric sticker.

2. Using an Indoor Model Outdoors Without Protection

After going over mistake #1, you may think you can’t use indoor models outdoors. You can install an indoor tankless water heater outside. But the mistake occurs when someone installs them without protection in the form of an outdoor vent cap. See the picture below.

A vent cap for a tankless water heater

Why Is This a Problem?

Without the proper venting cap, you can get these things clogging your water heater:

• Small animals
• Bees
• Bugs
• Spiders
• Leaves
• Trash

How can you tell if you don’t have a vent cap? Look on the top of your tankless water heater to see if:

• There’s a hole, exposing the inside of you tankless to the elements
• Something’s covering the vent cap connection

3. Installing B-Venting into an Indoor Tankless Water Heater

Using a B-vent for indoor tankless water heaters is another installation mistake.

Why Is This a Problem?

B-vents can get hot, so using them indoors can put you at risk of a fire.

How can you tell if you have a B-vent installed into your indoor tankless water heater? Look for:

• Green discoloration on your venting pipes.
• Scorch marks where your venting meets your walls.

4. Undersizing Tankless Water Heaters

Tankless water heaters need to be sized specifically for your water needs in the form of gallons per minute (GPM). If an installer doesn’t consider this, they will install your tankless water heater incorrectly.

Why Is This a problem?

If your tankless water heater is undersized, it will suffer from stress. Putting too much pressure on your water heater can lead to it breaking down for good.

How can you tell if your tankless water heater is undersized? Look for these signs:

• Low water pressure
• Stop and go hot water
• Water problems when you use multiple fixtures

A Noritz EZ 111 tankless water heater with an 11.1 GPM. In the right conditions, this tankless could serve a big family.

5. Undersizing Gas Line Piping

Another way installing tankless water heaters can go wrong is by using the incorrect size pipe for the gas line.

Why Is This a Problem?

If your gas line is undersized for your tankless model, it will not heat your water.

How can you tell if your gas line is undersized? Look for:

• Ignition issues – Your tankless water heater’s burner won’t light.
• Combustion issues – Your tankless water heater’s burner won’t stay lit.

Inside a Takagi tankless water heater

As you can see, the gas line leads straight to the burner. If there’s not the right amount of gas, you will not get hot water.

6. Crossing Water Lines

An easy-to-miss but vital mistake someone can make when installing a tankless water heater is crossing the water lines. What we mean by this is that the water lines pass too close to each other.

Why Is This a Problem?

If you have crossed water lines, your water will never get fully hot or cold.

How can you tell if you have crossed water lines?

• You have lukewarm water all the time.
• The hot water pipe is colder near the cold water line.
• The cold water pipe is warmer near the hot water line.

A Noritz tankless water heater and the water lines

In this picture, you can see the hot water line (indicated by the red knobs) and the cold water line (indicated by the blue knobs). You can check here to see if you have crossed pipes.

7. Isolation Valve Installation Issues

Isolation valves are valves used to flush or clean your tankless water heater. Sometimes, these valves are installed upside down or not at all!

Why Is This a Problem?

Tankless water heaters require yearly maintenance to function correctly. If you don’t have isolation valves or they’re upside down, you won’t be able to maintain your water heater. If you don’t maintain your tankless, it will break down due to minerals in the water.

How can you tell if you have isolation valve issues?

• Inspect your water heater.
• Check to see if you have red and blue isolated valves.
• Check to see if the small valves are on top.

Isolation valves

8. Tankless Water Heater Protection

The last point in our list is one we see the most often. Without protective devices, a tankless water heater is installed wrong.

Why Is This a Problem?

Tankless water heaters deal with heating city water every day. Because of that fact, tankless water heaters are exposed to high pressures and minerals in the water.

How can you tell if you don’t have protection on your tankless water heater? Look to see if you have all of the above.

Pressure Relief (Regulator) Valve

The pressure relief valve keeps the water pressure at a safe level. The city code is under 80 PSI.

Expansion Tank

An expansion tank helps protect your system from pressure spikes. If the city works on the mainline water and turns it back on, an unprotected system can leak or break down. Expansion tanks also relieve water pressure that builds up in the water tank as you heat water.

Water Filtration

To combat minerals in the water, make sure you have one of the following:

• Heater treater
• Water softener
• Flow-Tech
• Whole-house water filter

Note: Some owners choose not to add any of these devices to their tankless water heaters, but it can void the warranty.

A tankless water heater with an expansion tank, Flow-Tech, and a heater treater.

Next Steps if Your Tankless Water Heater’s Installed Wrong

Tankless water heaters are high-tech machines with a computer board and many delicate parts. Because of this fact, tankless water heater installers need to train on correct procedures and why they’re essential. Without the proper knowledge, water heater installers can leave you to deal with all of the problems we’ve talked about, if not more.

The complex inner workings of two Navien tankless water heaters

If you found some of these mistakes with your tankless water heater installation, act now to prevent adverse health effects, damage to your home, early death of your water heater, and frustrating tankless issues. Not to mention, you’ll save yourself time and stress by dealing with these problems that should have never happened in the first place.

Call your installer and get these issues fixed. Use this guide and your tankless water heater manual to advocate for yourself.

If you want to be prepared to talk to your tankless installer, read more about some of the topics we’ve discussed in this article:

• 3 Steps to Determine Which Size Tankless Water Heater You Need
• 2 Types of Tankless Water Heater Maintenance: Why They’re Important
• The 4 Steps To Flushing a Tankless Water Heater
• Water Filtration: Water Softener vs. Flow-Tech

Finally, if you need help figuring out if your tankless water heater is installed correctly, or you don’t want to deal with your installer again, call us at (818) 213-1773. We’ll make sure you’re safely set up, and we will walk you through everything, so you never have to deal with these worries again.