Navien tankless water heater error E110: abnormal air pressure

By Jason Dearmin · Last reviewed November 14, 2026 · How we check facts

What E110 means

Navien's NPN user manual (section 5.2) lists E110: Abnormal air pressure with a single action: "Ensure that the vent pipe is free of obstructions." The manual lists several other fan and air-volume codes (E109, E127, E157) as "contact Technical Support", so E110 is the one in this family where Navien expects you to check the vent first.

What to look at

• From the ground, check the outdoor exhaust and intake terminations for snow, ice, leaves, nests or anything covering them.
• Make sure nothing has been stacked, planted or built against the termination.
• Do not remove or open any vent piece. If you cannot see an obstruction, a technician should inspect the vent.

Freeze-protection note from the same manual

Navien's section 4.5 says freezing damage is most likely to happen through back-drafting caused by negative pressure in the building, strongly recommends direct-vent exhaust and intake piping, and says the optional recirculation mode is for freeze protection. It also says to not unplug the power cord, because the freeze protection function needs electricity, and not to close the gas valve except for routine maintenance. Those are the winter habits worth keeping.

Safe homeowner checks for Navien E110

1. Inspect outdoor terminationsFrom the ground, look at the exhaust and intake pipe ends and clear snow, ice or debris you can safely reach.
2. Reset the unit oncePress Reset on the front panel once after the vent is clear.
3. Call a technician if it returnsIf E110 returns, contact an authorized technician or Navien Technical Support.

Frequently asked questions

Will E110 clear by itself once the snow melts?

It can, if a blocked termination was the cause. The manual's only listed action is to ensure the vent pipe is clear; if the code remains after that, have it inspected.

Should I unplug the water heater to reset it in winter?

Navien's manual says not to unplug the power supply cord except for routine maintenance, because freeze protection needs electricity. Use the front-panel reset instead.

Sources

• User's Information Manual: NPN Non-Condensing Water Heaters, section 5.2 Understanding Error Codes (Navien) Covers: Navien NPN-series non-condensing tankless water heaters (NPN-120E through NPN-199U). Condensing NPE/NCB models have their own manuals.

Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.