Navien E110 Error Code

What does Navien E110 mean?

E110 means the air pressure differential switch has detected that combustion air pressure is outside acceptable limits. The unit monitors both intake and exhaust pressure to ensure complete combustion; when a blockage, clogged filter, or condensate trap issue disrupts the pressure balance, the PCB shuts down the burner and logs E110. The exhaust pipe, intake air filter, and condensate drain are the first systems to inspect.

Symptoms

• Unit shuts down with E110 and will not restart until the fault clears.
• No hot water production; burner does not ignite.
• Error occurs more frequently in winter when exterior vents may ice over.
• Condensate drain may be overflowing or backed up.

Common causes

• Exhaust vent blocked by debris, ice, or foreign objects at the exterior termination.
• Intake air filter clogged with dust, lint, or insulation fibers.
• Condensate trap blocked, preventing proper drainage and creating back-pressure.
• Damaged or disconnected vent pipe section creating a pressure leak.
• Air pressure differential switch itself has failed.

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Diagnostic steps

1. Inspect the exterior vent terminations

   Check both the intake and exhaust pipe ends at the exterior wall or roof. Remove any bird nests, debris, ice accumulation, or leaves. In freezing climates, verify the exhaust cap is not forming an ice dam that blocks flow.

2. Clean the intake air filter

   Remove the intake air filter (located at the bottom of the unit on most NPE/NPN models) and clean it thoroughly. Navien recommends cleaning this filter every 3–4 months in normal conditions and more frequently in dusty environments.

3. Clear the condensate drain and trap

   Locate the condensate drain line at the bottom of the unit. Flush the trap with clean water to dissolve any crystallized scale. Confirm the drain line runs freely to a floor drain — a blocked condensate path creates back-pressure that trips the air pressure switch.

4. Inspect vent pipe joints and routing

   Walk the entire vent run and press each push-fit or twist-lock joint to confirm it is fully seated. Check for pipe sections that may have shifted, sagged, or been physically damaged after installation.

5. Test the air pressure switch

   If all vent and filter checks pass, use a manometer to verify the pressure switch is opening and closing at the correct differential pressure spec from the service manual. Replace the switch if it does not operate within spec.

When to call a professional

If E110 persists after clearing vents, cleaning the air filter, and flushing the condensate trap, a technician should perform a full combustion air flow test and measure static pressure at the switch ports. Air pressure switch replacement and vent system leak testing require access to pressure measurement tools not typically available to non-certified technicians.