Navien recalls this tankless water heater and two others.

Navien has recalled 3,400 tankless water heaters and boilers because a kit used to convert them from running on natural gas to propane can cause them to produce excessive amounts of carbon monoxide, posing a risk of CO poisoning.

Called the invisible killer because you can’t see or smell it, CO is responsible for 400 deaths a year, according to the Centers for Disease Control. No incidents have been  associated with this recall.

Tankless, or on-demand water heaters, heat water as it’s being used and are an alternative to storage-tank water heaters. They can run on natural gas, propane, or electricity. When gas or propane are used, the heater must be vented to the outdoors  to remove the byproducts of combustion.

The recall, announced by the Consumer Product Safety Commission, involves two models of Navien condensing water heaters, the NPE-180A and the NPE-180S, and one model of a Navien condensing combination boiler, the NCB-180E.

They were sold directly to Navien installers and not in consumer home improvement stores. Manufacturers recommend that tankless water heaters be professionally installed.

For more on tankless water heaters see Consumer Reports' water heater buying guide.

Recall Details

The recall: About 3,400 NPE-180A and the NPE-180S Navien condensing tankless water heaters and NCB-180E condensing combination boilers. See the recall notice for the full list of serial numbers.

The risk: A kit installed on the tankless water heaters and boilers to convert them from natural gas to propane can cause the unit to produce excessive amounts of carbon monoxide, posing a risk of carbon monoxide poisoning to consumers.

Incidents/injuries: None

Where and when sold: At wholesale distributors to installers nationwide from August 2018 through October 2018 for about $1,400 to $1,700 for water heaters and $3,800 for combination boilers.

The remedy: Consumers should stop using the recalled water heaters and boilers that run on propane gas and contact Navien for a free replacement conversion kit. Consumers who continue use of the water heaters and boilers while awaiting repair should have a working carbon monoxide alarm installed outside of sleeping areas in the home.

Contact the manufacturer: For more information, call Navien at 800-244-8202; e-mail recall@navien.com or visit Navien’s website.

Report a defective product: Call the CPSC hotline at 800-638-2772 or go to saferproducts.gov.