What causes Navien Tankless Water Heater / Combi Boiler E110 / 110 / 110E?

A clogged air intake filter. Navien's user manuals name this directly as a cause of Error Code 110 and say to clean the filter every 3 to 4 months. A blocked exhaust or air intake vent, for example snow, leaves, nests or debris at the outside termination. Water collected inside the air supply or exhaust pipe, which the NPE service manual says can happen with an improperly installed vertical intake pipe. A clogged, kinked or frozen condensate drain line or trap, which backs up into the exhaust. The service manual lists this as a cause of 110E. A clogged venturi (burner) hole, listed first on the NPE service manual's E110 check list. Exhaust gas getting pulled back into the air supply pipe because of the way the vent was installed, which the service manual says can cause abnormal combustion and E110. A broken or clogged air pressure sensor hose, a defective air pressure sensor, or a control board (PCB) problem.

How do I fix Navien Tankless Water Heater / Combi Boiler E110 / 110 / 110E?

Turn the unit off with the Power button and disconnect its power supply before opening it. Clean the air intake filter the way Navien's NPE manual describes: remove the front cover, remove the screw holding the filter assembly (top left on NPE and NPE-2 heaters), pull it out, take the filter out of its plastic holder, and clean it with a toothbrush under clean running water. On NCB combi boilers the cover is held by 3 buckles instead. Let the filter dry completely, put it back in its holder, reinstall it with the screw, replace the cover, restore power, and turn the unit back on. Go outside and check the exhaust and intake vent terminations. Clear away snow, ice, leaves, nests or anything blocking them. Navien's service manual says terminations should sit at least 12 inches above the highest expected snow line, or higher if local code requires. Check the condensate drain hose for kinks or ice, and make sure it drains freely to the floor drain or neutralizer. Run hot water again. If E110 comes right back after the filter is clean and the vents are clear, stop resetting it and call for service.

When should I call a pro for Navien Tankless Water Heater / Combi Boiler E110 / 110 / 110E?

E110 returns after the intake filter is cleaned and the vents and condensate drain are clear. Navien's user manuals give Technical Support at 1-800-519-8794 for problems the listed remedies don't fix. Inspecting the venturi, the air pressure sensor and its hose, and checking sensor voltages. The NPE service manual lists a 5 V supply and a 0.3 to 4.5 V signal on the air pressure sensor. Comparing fan speed against the standard values at minimum and maximum firing, which the service manual uses to tell a blockage apart from a sensor or board fault. Removing and cleaning the condensate trap, or fixing vent pipe slope, length or termination problems. Venting on a gas appliance should be corrected by a licensed installer. The unit is still under warranty. Navien says to contact Technical Support first for warranty service, or the installer who put the unit in.

Code: E110 / 110 / 110E🚿 Navien Tankless Water Heater / Combi Boiler

Navien Error Code E110 (110E): Abnormal Air Pressure, Clogged Intake Filter or Blocked Vent (Meaning, Causes, Fixes)

Q: What does Navien Tankless Water Heater / Combi Boiler E110 / 110 / 110E mean?

E110 on a Navien tankless water heater or combi boiler means abnormal air pressure: the unit isn't getting the airflow it expects through the burner. Navien's user manuals say the most common cause is a clogged air intake filter, and that the exhaust pipe should be checked for obstructions. If cleaning the filter doesn't clear it, Navien's service manual points to a blocked vent, a clogged condensate drain, or a bad air pressure sensor. Navien's User's Information Manuals for the NPE and NPE-2 tankless water heaters and the NCB-E combi boilers list E110 as Abnormal air pressure, with two remedies: ensure that the exhaust pipe is free of obstructions, and clean the intake air filter. The same manuals say that if the air intake filter gets clogged by dust or lint, the unit will stop operating and show Error Code 110. According to the NPE service manual, the control compares the air pressure sensor (APS) reading and the fan speed, and shows 110E when the initial fan auto-adjust can't be completed, or when the unit is firing at up to 95% of maximum and the air pressure sensor doesn't reach its standard value. In plain terms, something is choking the airflow in or out of the unit, or the sensor that measures it has failed. E109 (abnormal fan motor operation) shares the same first checks.

Reviewed 2026-10-22 · Based on 4 manufacturer & service sources

What the code means

Navien's User's Information Manuals for the NPE and NPE-2 tankless water heaters and the NCB-E combi boilers list E110 as Abnormal air pressure, with two remedies: ensure that the exhaust pipe is free of obstructions, and clean the intake air filter. The same manuals say that if the air intake filter gets clogged by dust or lint, the unit will stop operating and show Error Code 110. According to the NPE service manual, the control compares the air pressure sensor (APS) reading and the fan speed, and shows 110E when the initial fan auto-adjust can't be completed, or when the unit is firing at up to 95% of maximum and the air pressure sensor doesn't reach its standard value. In plain terms, something is choking the airflow in or out of the unit, or the sensor that measures it has failed. E109 (abnormal fan motor operation) shares the same first checks.

Likely causes

A clogged air intake filter. Navien's user manuals name this directly as a cause of Error Code 110 and say to clean the filter every 3 to 4 months.
A blocked exhaust or air intake vent, for example snow, leaves, nests or debris at the outside termination
Water collected inside the air supply or exhaust pipe, which the NPE service manual says can happen with an improperly installed vertical intake pipe
A clogged, kinked or frozen condensate drain line or trap, which backs up into the exhaust. The service manual lists this as a cause of 110E.
A clogged venturi (burner) hole, listed first on the NPE service manual's E110 check list
Exhaust gas getting pulled back into the air supply pipe because of the way the vent was installed, which the service manual says can cause abnormal combustion and E110
A broken or clogged air pressure sensor hose, a defective air pressure sensor, or a control board (PCB) problem

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Turn the unit off with the Power button and disconnect its power supply before opening it.
Clean the air intake filter the way Navien's NPE manual describes: remove the front cover, remove the screw holding the filter assembly (top left on NPE and NPE-2 heaters), pull it out, take the filter out of its plastic holder, and clean it with a toothbrush under clean running water. On NCB combi boilers the cover is held by 3 buckles instead.
Let the filter dry completely, put it back in its holder, reinstall it with the screw, replace the cover, restore power, and turn the unit back on.
Go outside and check the exhaust and intake vent terminations. Clear away snow, ice, leaves, nests or anything blocking them. Navien's service manual says terminations should sit at least 12 inches above the highest expected snow line, or higher if local code requires.
Check the condensate drain hose for kinks or ice, and make sure it drains freely to the floor drain or neutralizer.
Run hot water again. If E110 comes right back after the filter is clean and the vents are clear, stop resetting it and call for service.

🛠 When to call a pro

E110 returns after the intake filter is cleaned and the vents and condensate drain are clear. Navien's user manuals give Technical Support at 1-800-519-8794 for problems the listed remedies don't fix.
Inspecting the venturi, the air pressure sensor and its hose, and checking sensor voltages. The NPE service manual lists a 5 V supply and a 0.3 to 4.5 V signal on the air pressure sensor.
Comparing fan speed against the standard values at minimum and maximum firing, which the service manual uses to tell a blockage apart from a sensor or board fault
Removing and cleaning the condensate trap, or fixing vent pipe slope, length or termination problems. Venting on a gas appliance should be corrected by a licensed installer.
The unit is still under warranty. Navien says to contact Technical Support first for warranty service, or the installer who put the unit in.

Parts that commonly fix it

Always match the part number to your exact model.

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Soft toothbrush or small parts brush

What Navien's manual says to clean the air intake filter with, under clean running water.

[affiliate link slot: AFFILIATE_SLOT_CLEANING_BRUSH]

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Carbon monoxide alarm

A smart addition near any gas water heater or boiler, especially when the vent has been blocked. Navien's service manual notes a failing air pressure sensor can lead to excess carbon monoxide.

[affiliate link slot: AFFILIATE_SLOT_CO_ALARM]

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Navien air pressure sensor (exact part for your model)

Technician part only. Navien recommends troubleshooting and repair be done by qualified, licensed professionals.

[affiliate link slot: AFFILIATE_SLOT_TANKLESS_APS]

Sources

Last reviewed 2026-10-22. Always confirm against the manual for your exact model number.