Navien E046: limit control fault

The high limit switch is a safety device on the heat exchanger. If the temperature climbs past its limit, it opens and stops the burner. E046 means the control board has seen that switch report abnormal operation.

The meaning below comes from Navien's manuals for its NPE condensing tankless water heaters. Many codes are shared with Navien combi boilers, but check the manual for your model if something does not match.

For this code, Navien's user manual directs owners to contact Navien technical support (1-800-519-8794) or a licensed installer.

Two possibilities

The unit really overheated

Anything that keeps heat from moving into the water can push the heat exchanger too hot. Common reasons are scale inside the heat exchanger, a clogged cold water inlet filter and low water flow. If the unit has also shown E016 (heat exchanger overheating), this is the likely story.

The switch or wiring has failed

A switch that has worn out or a loose or broken wire can report a fault even when the temperature is normal. A technician tests the switch with a meter.

What you can do

• Clean the cold water inlet filter as described in the manual.
• Check your maintenance records. If the unit has not been flushed in a year or more with hard water, it is due.
• Reset the unit once. If E046 returns, call for service.

Why not bypass it

The limit switch exists to stop a runaway overheat. It should never be jumped or bypassed, even temporarily. Fix the cause or replace the switch.

See every code on our Navien error codes page.