Water Heater Codes

Navien E110: Exhaust Blockage

Hot water worked fine last week; now the unit won't fire and E110 sits on the display. Nine times out of ten in cold-weather months, the cause is sitting right outside on the exterior wall where the vent terminal lives.

Applies to: Navien NPE, NCB, and NHB tankless and combi/condensing water heaters

What it means

Exhaust Blockage — the unit has detected an obstruction in the exhaust venting. Extremely common in winter. Snow drifting against a low sidewall vent terminal, or a bird's nest built into one over the off-season, are two of the most frequently reported culprits behind this exact code.

Most common causes

What you can safely check yourself

  1. Check the outdoor vent terminal for snow, ice, leaves, or nesting debris and clear it if it's safely reachable
  2. Check and clean the intake air filter per your owner's manual

When to call a professional

The vent terminal isn't safely accessible, blockage keeps recurring, or the venting was recently installed/modified and may be undersized or improperly pitched.

Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.

What the fix costs

Clearing a blocked vent terminal yourself costs nothing but time. If a technician needs to come inspect or re-pitch the venting, a diagnostic visit generally runs $150–$600 (Angi, Fixr), and if the vent itself needs to be re-run or resized because it was undersized to begin with, that's a labor-heavier job priced case-by-case by a local installer rather than a fixed national range.

Related codes

All Navien codes

Every Navien water heater fault code — the full list on one page.

Safety. A restricted exhaust vent on a gas appliance is a carbon-monoxide risk, not just an inconvenience. If the vent terminal isn't easily and safely reachable — a second-story wall, a steep roof, deep snow — don't improvise a way to get to it; call a licensed technician instead.

Sources

This site is an independent reference, not a substitute for a licensed plumber or electrician. Gas water heaters can leak carbon monoxide, leak gas, or catch fire if serviced incorrectly. Anything involving the gas line, gas control valve, venting, or main electrical wiring should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.