Thermocouple
Common pilot and ignition part on gas water heaters.
Navien Error Code E007 — What It Means
Navien E007 indicates abnormally high temperature at the hot water outlet — the outgoing domestic hot water (DHW) sensor read a temperature above the safe limit during operation. Navien tankless water heaters monitor the outlet temperature continuously; if it exceeds ~185°F (85°C) or rises faster than the unit’s safety algorithm allows, E007 trips the unit to prevent scalding or damage to the heat exchanger. This fault is more common during low-flow conditions where water moves slowly through the heat exchanger and absorbs too much heat.
Common Causes
- Very low water flow rate — Insufficient flow through the heat exchanger causes the water to absorb excessive heat; flow below the minimum activation rate is the primary cause.
- Scale buildup in the heat exchanger — Calcium and lime deposits reduce heat transfer efficiency and create hot spots in the heat exchanger passages.
- Faulty hot water outlet thermistor — The sensor drifts high or develops an intermittent fault, reporting falsely elevated temperatures.
- High incoming cold water temperature — In summer or in warm climates, cold water supply may be warm enough that the unit overshoots the set point.
Step-by-Step Fix
- Check flow rate — Open a hot water fixture fully and confirm flow is adequate. Navien units typically require a minimum of 0.5 GPM. A partially closed inlet valve or a clogged aerator can drop flow below minimum.
- Clean the inlet filter screen — Navien units have a small mesh filter screen at the cold water inlet. Turn off the water supply, remove the screen, clean it under running water, and reinstall.
- Flush the heat exchanger (descale) — If the unit is more than 2 years old or is in a hard-water area, flush the heat exchanger with a vinegar or citric acid solution using the service ports. Navien’s descaling kit connects directly to the unit.
- Lower the set point temperature — If the set point is above 140°F (60°C), try lowering it to 120–130°F. The unit may be running at maximum fire rate to reach a high set point with marginal flow.
- Test the outlet thermistor — With power off, disconnect the outlet sensor and measure resistance. Compare to Navien’s thermistor specification for your model. An out-of-range reading requires sensor replacement.
- Reset the unit — Press the reset button or cut power for 30 seconds. Restore and run a full hot water draw to confirm E007 is cleared.
Parts Often Needed
| Part | Notes |
|---|---|
| Outlet water temperature thermistor | Navien model-specific; matches DHW outlet sensor spec |
| Descaling kit | Pump + citric acid solution; available from Navien or HVAC supply houses |
| Cold water inlet filter screen | Inexpensive; keep a spare on hand |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Persistent E007 after descaling and confirming good flow may indicate a partially failed gas valve that’s not modulating properly, causing overcombustion. Gas valve service requires a licensed plumber or HVAC technician with Navien training.