Navien Water Heater Error Codes

Common Symptoms

• E001–E004 series — unit will not fire, no hot water
• E007 — unit attempts to ignite but fails repeatedly
• E010–E016 series — unit shuts down mid-cycle, overheating fault
• E030 — exhaust back-pressure, unit locks out
• E033–E038 series — temperature sensor fault, unit defaults to error state
• E047 — heat exchanger overheat from scale buildup
• E110 — freeze protection activated, reduced or no hot water
• Error code clears with power cycle but returns within hours

Most Likely Causes

1. 1

   E001 — No Ignition Signal (Gas Supply, Igniter, Flame Rod)

   E001 indicates the Navien control board did not receive an ignition confirmation signal after the initial ignition attempt. Diagnostic sequence: (1) Verify gas supply — check that the gas shutoff valve at the unit is fully open (handle parallel to pipe) and that other gas appliances in the home are working. If no other gas appliances are available, test gas pressure at the unit's inlet test port with a low-pressure manometer — natural gas static must be ≥3.5 inches WC, propane ≥8 inches WC. (2) Inspect the igniter electrode: look for ceramic cracks, carbon bridging across the ceramic, or a gap that is too large or too small (correct gap is 3–4 mm). Clean or replace. (3) Clean the flame sensing rod: carbon deposits on the metal sensing surface produce a false 'no flame' signal. Clean with 400-grit emery cloth. E001 and E003 share the same root causes — E001 is the first failed attempt, E003 is after three consecutive failures (lockout).

2. 2

   E002 — Ignition Device Fault (Igniter Circuit)

   E002 indicates the Navien control board detected a fault in the ignition device circuit itself — distinct from E001/E003 which indicate failure to establish a flame. E002 typically points to: (1) A failed igniter electrode — the ceramic has cracked internally and the spark is shorting to the electrode body rather than bridging the spark gap. Replace the igniter assembly. (2) A broken igniter wire harness — the high-voltage igniter lead has a break or damaged insulation that prevents the spark discharge. Inspect the igniter cable from the control board to the electrode; replace if cut, cracked, or if the connector pins show burn marks. (3) A failed ignition module on the control board (PCB) — if the igniter assembly and harness test good, the PCB ignition circuit has failed. PCB replacement is a factory service procedure.

3. 3

   E003 — Ignition Failure (3 Consecutive Attempts — Full Lockout)

   E003 is the full lockout code — the Navien attempted ignition three consecutive times without establishing a stable flame and has locked out for safety. It does not reset automatically; a manual power cycle is required. E003 is the most common Navien error code and shares root causes with E001: gas supply pressure insufficient, gas shutoff valve not fully open, flame sensor rod contaminated, igniter electrode faulty, or minimum water flow rate below 0.5 GPM (unit will not fire without adequate flow). On Navien units with the NaviLink module, check the fault log in the Navien app — if E003 appears repeatedly at the same time of day (e.g., morning peak demand), gas supply pressure is likely dropping under simultaneous multi-appliance load rather than being a hardware fault.

4. 4

   E004 — False Flame Detection (Flame Sensor Detecting Signal When Burner Is Off)

   E004 means the Navien flame sensor is detecting an ionization signal when the burner should be off — a false flame that prevents ignition as a safety measure. Causes: (1) Residual condensate or moisture on the flame sensor rod creating a conductive path that mimics the ionization signal. Remove the flame sensor rod, dry it with compressed air, and allow 30 minutes for moisture to evaporate. (2) Cracked ceramic insulator on the flame sensor allowing the rod to contact the unit chassis at one point — measure resistance between the rod and the chassis with a multimeter; any reading below 1 MΩ indicates a conductive path. Replace the flame sensor assembly. (3) PCB input circuit fault — if the sensor checks out electrically, the control board's flame detection input circuit has failed.

5. 5

   E007 — Hot Surface Igniter Fault

   E007 indicates the hot surface igniter (HSI) circuit has detected a fault. Navien models using a hot surface igniter (rather than a spark igniter) will display E007 when the HSI element resistance is out of specification or the element has failed. Measure resistance across the HSI element terminals — a cold HSI element typically reads 40–100 ohms; an open reading (OL) indicates a failed element. Replace the hot surface igniter assembly. Also check the HSI wire harness for damaged insulation or broken connector pins. On units where the HSI is integral to the igniter assembly, replace the full assembly.

6. 6

   E010 — Overheat Cut-Off Fuse (High Limit Safety Device)

   E010 on Navien indicates the overheat cut-off fuse (thermal fuse or high-limit thermostat) has tripped or failed. This is a one-time safety device located on the heat exchanger assembly that opens the circuit when the heat exchanger reaches an unsafe temperature, typically above 194°F. E010 can be triggered by: (1) Severe scale buildup causing localized overheating (address scale first — see E047). (2) A blocked condensate drain causing steam back-pressure into the heat exchanger area. (3) Extended low-flow operation where water was recirculated through the heat exchanger without sufficient makeup flow. After addressing the root cause, the thermal fuse must be tested with a multimeter (continuity check). If open, replace the thermal fuse or high-limit thermostat before restarting. This is a model-specific part — order by Navien model and serial number.

7. 7

   E011 — Heat Exchanger Overheat (Primary Exchanger High Limit)

   E011 indicates the primary heat exchanger has exceeded its safe operating temperature limit — the thermistor or dedicated overheat sensor at the primary exchanger detected an over-temperature condition. Causes mirror E047 (scale buildup) but specifically reference the primary (non-condensing) heat exchanger. In dual heat exchanger Navien models, E011 points to the upper/primary circuit while E047 points to the secondary/condensing circuit. Descale both exchangers simultaneously per the annual maintenance procedure. If E011 recurs immediately after descaling, the primary heat exchanger thermistor may have drifted out of calibration — replace the thermistor per the model service manual.

8. 8

   E012 — Flame Loss During Operation

   E012 means the Navien ignited successfully but the flame was lost during the heating cycle. The three main causes in order of frequency: (1) Dynamic gas pressure drop — under full firing load (up to 199,900 BTU/hr on the largest NCB/NHB models), supply line pressure drops below the 3.5 inches WC minimum; measure manifold pressure during firing, not just static pressure. (2) Degraded flame sensor rod — a partially contaminated sensor maintains the ionization signal at the low BTU of ignition but loses it as thermal expansion shifts the rod position at higher output. Clean the rod. (3) Partial vent blockage — enough to allow ignition at low BTU but insufficient combustion air at full output. Inspect the vent run and termination cap.

9. 9

   E015/E016 — Thermal Fuse (Secondary Heat Exchanger Circuit)

   E015 and E016 indicate thermal fuse faults in the secondary heat exchanger circuit. E015 is the secondary exchanger thermal fuse fault; E016 is the secondary heat exchanger overheat. Both codes point to the condensing (secondary) heat exchanger and share the same root cause as E047: calcium scale buildup causing localized overheating that eventually trips the secondary thermal fuse. Repair sequence: (1) Descale both heat exchangers. (2) Test the secondary thermal fuse with a multimeter for continuity — replace if open. (3) If fuses repeatedly trip after descaling, inspect for a failing condensate drain (back-pressure causing steam to accumulate in the secondary exchanger area) or an undersized gas supply providing a lean-burning flame that elevates exhaust temperatures.

10. 10

    E030 — Exhaust Blockage (Vent or Condensate Drain Back-Pressure)

    E030 is the exhaust pressure sensor fault — the combustion fan cannot achieve the required exhaust flow rate. On Navien condensing models, the condensate drain is the most common cause: a kinked or clogged condensate drain tube, a clogged condensate neutralizer, or a dry drain trap creates back-pressure in the condensate collection chamber, which is mechanically coupled to the exhaust pressure circuit. Inspection sequence: (1) Condensate drain tube — trace from unit to floor drain; confirm continuous downward slope, no kinks, no loops, no blockage at the outlet. (2) Condensate neutralizer — inspect media; replace if spent or clogged. (3) Vent run — inspect the full vent pipe from unit to termination cap; count equivalent length; check exterior cap for debris, ice, or bird nests. (4) Vent pipe diameter and material — must match installation manual specification (typically PVC Schedule 40 or CPVC; not ABS).

11. 11

    E033/E034/E035/E036 — Thermistor Faults (Inlet, Outlet, Heat Exchanger, DHW)

    E033 is the cold water inlet thermistor fault; E034 is the hot water outlet thermistor fault; E035 is the heat exchanger thermistor fault; E036 is the DHW (domestic hot water) outlet thermistor fault on combi-boiler models. Thermistors are NTC (negative temperature coefficient) sensors that change resistance with temperature — a disconnected, open, or shorted thermistor produces a fault code. Diagnosis: disconnect the thermistor connector at the PCB and measure resistance at room temperature (68°F); a healthy Navien thermistor typically reads approximately 10,000 ohms (10 kΩ) at 68°F. An open reading (OL) or a near-zero reading indicates the thermistor has failed and requires replacement. Also inspect the thermistor wire harness for damage at the connector pins.

12. 12

    E037 — Air Pressure Switch Fault

    E037 indicates the combustion air pressure switch has not closed (or has opened unexpectedly), meaning the combustion fan is not producing sufficient air pressure differential to confirm proper operation. Causes: (1) Condensate in the pressure switch hose — drain the hose; condensate should not pool in the switch circuit. (2) Blocked air intake — check the air intake vent termination for obstruction. (3) Failed combustion fan (venter) — measure fan motor voltage at the harness with the unit firing; if voltage is present but the fan is not spinning at full speed, the fan motor has failed. (4) Stuck air pressure switch diaphragm — the switch can stick open or closed after condensate contamination; replace if confirmed.

13. 13

    E038 — Exhaust Thermistor Fault

    E038 indicates the exhaust thermistor (flue temperature sensor) has detected a value outside the expected range, or the thermistor circuit is open/shorted. The exhaust thermistor monitors exhaust gas temperature as a secondary safety check — extremely high exhaust temperatures can indicate a blocked vent or a severely scaled heat exchanger. Diagnosis: disconnect the exhaust thermistor connector and measure resistance at ambient temperature — should read approximately 10 kΩ at 68°F. Replace if open or shorted. Also verify the vent pipe is not blocked — a blocked vent causes genuine high exhaust temperatures that the thermistor is correctly detecting.

14. 14

    E040 — Cascade Communication Fault

    E040 appears on Navien units installed in a cascade (multiple units linked together to increase total BTU capacity for large commercial or residential applications). It indicates a communication error between the master unit and one or more secondary units on the cascade bus. Causes: damaged or disconnected CAT5 communication cable between units; an address conflict (two units set to the same address); or a failed communication module on one of the units. Diagnosis: verify CAT5 connections at both ends for each unit in the cascade; check dip switch settings on each unit to confirm unique unit addresses; power cycle all units simultaneously. If E040 persists, identify the failing unit by disconnecting secondary units from the cascade one at a time.

15. 15

    E047 — Heat Exchanger Scale Overheat (Descale Required)

    E047 is the secondary heat exchanger overheat fault — specifically from calcium carbonate scale accumulation in the condensing heat exchanger of NCB/NHB/NPE units. Hard water (above 7 grains per gallon or 120 ppm TDS) deposits scale inside the heat exchanger tubes over 1–3 years, progressively reducing flow and creating localized hot spots. E047 initially appears under high-demand conditions; as scale worsens, it occurs at lower and lower BTU loads. Hot water output decreases measurably, and the unit produces a popping or kettling sound during heating. Fix: descale both heat exchangers using the Navien service port procedure with white vinegar (3 gallons undiluted, 60–90 minutes) or CLR solution. Install an inline scale inhibitor or water softener to prevent recurrence. Annual descaling prevents E047 from ever occurring.

16. 16

    E110 — Freeze Protection Activated

    E110 indicates the Navien unit's freeze protection circuit has activated — the ambient temperature around the unit has dropped to the freeze protection threshold. The unit activates internal components (circulates water, energizes heat) to prevent freezing. E110 is an informational code rather than a lockout — the unit should resume normal operation when ambient temperature rises above the threshold. However, E110 in combination with any other error code indicates the unit may have experienced partial freeze damage. If E110 appears regularly, the unit is installed in an environment that is too cold without adequate insulation or supplemental heat. Actions: insulate the space, insulate the inlet/outlet pipes, verify the unit has continuous power (freeze protection requires power), and set the freeze protection temperature to the highest setting in the Navien app. If E110 appeared after a power outage during a freeze, inspect all water connections and the heat exchanger for freeze cracks before restoring operation.

Quick DIY Checks

1. 1Step 1 — Record the error code and check the Navien app fault log: press the INFO button on the unit panel to display the current error code clearly. On units with the NaviLink Wi-Fi module, open the Navien app (iOS/Android), navigate to the unit, and view the full fault history — this shows every error code, when it occurred, and how many times. The fault history is essential for pattern diagnosis: E003 recurring every morning suggests a gas pressure issue during peak demand; E030 appearing only on rainy days suggests condensate drain surge. Screenshot or photograph the fault log before proceeding. For units without NaviLink, record the displayed code and note whether the unit locked out completely (requires manual reset) or self-cleared.
2. 2Step 2 — Perform a power cycle reset (for E001–E016, E030, E033–E038, E047): a power cycle reset clears the fault and allows one additional ignition attempt — it does not fix the underlying cause, but confirms whether the fault is persistent or intermittent. Procedure: (a) Press the POWER button on the unit panel to turn the unit off. (b) Unplug the unit from the wall outlet (or switch off the dedicated circuit breaker). (c) Wait 30 seconds with the unit fully unpowered — this fully clears the control board's fault latch. (d) Plug back in (or switch breaker on). (e) Press POWER to turn the unit on. (f) Open a hot water tap and attempt a draw. If the unit fires and heats successfully, the fault was intermittent. If the same error code returns within 1–3 firing cycles, the root cause is still present and must be addressed per the specific code steps in this guide. Note: E040 (cascade) requires powering all cascade units simultaneously.
3. 3Step 3 — E001/E002/E003/E007: verify gas supply and clean igniter/flame sensor: the diagnostic sequence for all ignition-related codes is identical. (1) Gas supply: confirm gas shutoff valve is fully open; test static gas pressure with a manometer at the unit inlet test port (natural gas ≥3.5 inches WC static, propane ≥8 inches WC). (2) Flame sensor rod: remove from the burner assembly (1 mounting screw), inspect the metal tip for carbon deposits or oxidation, clean with 400-grit emery cloth until bright metal is visible. Reinstall. (3) Igniter electrode: inspect the ceramic body for cracks; measure the electrode gap (3–4 mm); replace the igniter assembly if the ceramic shows cracks or the gap cannot be corrected. (4) E002/E007: specifically test igniter continuity — measure resistance across the igniter terminals; an open reading (OL) means the element or circuit has failed. Replace the igniter or HSI element.

1. 4Step 4 — E010/E011/E015/E016: check and replace thermal fuse, then descale: thermal fuse codes indicate a safety device has tripped. Before replacing the fuse, address the root cause: (1) Descale both heat exchangers per Step 5 below. (2) Verify condensate drain is clear (Step 6 below). (3) After addressing root cause, shut off power and gas; locate the thermal fuse or high-limit thermostat on the heat exchanger assembly per the model-specific service manual; test with a multimeter in continuity mode — a blown fuse reads OL (no continuity). Order the Navien model-specific replacement thermal fuse; install per service manual instructions. Replacing the fuse without fixing the scale or drain blockage root cause will result in the new fuse tripping within days.
2. 5Step 5 — E047 (and preventive maintenance): descale the dual heat exchanger: the annual heat exchanger descale is the single most impactful maintenance procedure for Navien condensing units — it prevents E047, E011, E016, and reduces E030 from condensate back-pressure. Requirements: isolation service valves on hot and cold connections at the unit (have a plumber install them if absent — this is a permanent installation requirement, not a temporary procedure). Equipment: submersible acid-rated pump, 5-gallon bucket, two hose lengths, 3 gallons of undiluted white vinegar or CLR solution. Procedure: (1) Close cold water supply. (2) Close both service isolation valves. (3) Connect pump to cold-side service port; return hose from hot-side service port to bucket. (4) Open both service valves. (5) Run pump for 60–90 minutes. (6) If solution turns milky and stops producing bubbles before 60 minutes, drain and replace with fresh solution. (7) After full cycle: close service valves, disconnect pump, flush with 5 minutes of clean water. (8) Restore normal operation and verify no E047 within 3 firing cycles.
3. 6Step 6 — E030: clear condensate drain, inspect neutralizer, check vent: (1) Condensate drain tube: trace the 1/2-inch flexible tube from the unit outlet to the floor drain. It must slope continuously downward — no uphill sections, kinks, or loops. Disconnect at the unit barb fitting and blow compressed air through toward the floor drain. (2) Condensate neutralizer: if a neutralizer housing is installed, open the top and inspect the marble chip or calcium carbonate media. Replace media if it is black, slimy, or if the media level has significantly dropped (media is consumed over time). A clogged neutralizer creates back-pressure that triggers E030 even when the vent is clear. (3) Vent termination: go outside and inspect the PVC vent cap for debris, bird nests, or ice. Remove any obstruction. On concentric vent caps, confirm both the inner exhaust discharge and outer air intake annulus are clear.
4. 7Step 7 — E033/E034/E035/E036/E037/E038: diagnose and replace faulty thermistor or pressure switch: thermistor faults require measuring resistance at the specific sensor. (1) Identify the thermistor associated with the fault code per the model-specific wiring diagram in the Navien installation manual. (2) Shut off power and gas. (3) Disconnect the thermistor electrical connector. (4) Measure resistance between the two thermistor terminals with a multimeter at room temperature (approximately 68°F). Normal reading for Navien NTC thermistors: approximately 10,000 ohms (10 kΩ) at 68°F. An open reading (OL) or near-zero reading indicates a failed thermistor — order the model-specific replacement. For E037 (air pressure switch): disconnect the pressure switch hose and check for condensate pooling inside the hose (drain it). Replace the pressure switch if the condensate drain is clear and E037 persists.
5. 8Step 8 — Condensate neutralizer maintenance schedule: Navien condensing units require regular condensate neutralizer maintenance to maintain E030-free operation and comply with plumbing codes. Maintenance schedule: (1) Monthly — visually inspect the drain tube for kinks or blockage. (2) Every 6 months — open the neutralizer housing and visually inspect the media; test pH of the condensate exiting the neutralizer with pH paper (should be ≥6.0). (3) Annually — replace the neutralizer media regardless of appearance; media consumption rate depends on firing hours, not elapsed time, but annual replacement is conservative and reliable. If the unit fires continuously for space heating (combi-boiler mode), replace neutralizer media every 6 months. Use only marble chips or calcium carbonate media specified for condensate neutralizers — do not substitute limestone gravel or other calcium-containing materials, which may have the wrong particle size and void the housing warranty.

Repair vs Replace

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