Tankless Water Heaters & Safety

Tips and support to ensure your home's tankless water heater safety.

A. O. Smith has provided innovative and safe water heaters for your home for over 80 years. Though your water heater may not be at the top of your mind on a daily basis, understanding safety precautions during use and installation is important. Through engineering and technology, A. O. Smith water heaters are vigorously tested and designed with features that can detect problems before they occur. See below for a list of innovative safety features that A. O. Smith builds into all tankless water heaters.

How We Keep Your Water Heater Safe

Diagram of the interior of a tankless water heater.

Air-Fuel Ratio (AFR) Sensor

By monitoring and maintaining proper combustion at all times, your tankless water heater will adjust its fan speed to make sure that air and fuel are mixed at the right ratio. This minimizes emissions and maximizes efficiency.


Your indoor condensing water heater monitors exhaust temperatures to operate at safe levels for PVC venting. If these near an unsafe level, the thermistor and hi-limit switch regulate combustion and can even shut the heater down to protect the vent material.

Hi-Limit Switch

This feature helps to ensure water temperatures do not exceed safe levels. Inlet and outlet thermistors measure water temperatures to make sure the heater isn't overheating the water. If the water temperature exceeds 185° F or 194° F, depending on the model, the hi-limit switch disengages gas valves, which effectively shuts down your tankless water heater.

Freeze Protection

Tankless water heaters have an internal freeze protection system. All models come standard with electric heaters, and some have an added system to fire the burner for a few seconds. This prevents the heat exchanger from falling below a certain temperature and reduces the chances of freeze damage. However, we recommend that any tankless heater installed in a cold climate be installed indoors so that it is not directly subjected to freezing temperatures.

Overheat Cut Off Fuse

Tankless water heaters are built with an overheat cut off fuse to help protect your water heater. It is a safety feature that disengages the gas valve if the wire is cut from a breach in the heat exchanger wall or failed gaskets around the combustion box.

Additional Reading

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