Heating supply thermistor open or short circuit Auto Water Supply
The E205 error code on Navien boilers indicates heating supply thermistor open or short circuit auto water supply. Symptoms include displays ‘205e’ on the front panel. if this occurs, the boiler shuts down, check the temperature displayed on the front panel.
Navien E205 means: heating supply thermistor open or short circuit auto water supply. The usual causes are including leakage or faulty sensor. You can safely reset the boiler once — if E205 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does E205 Mean
The E205 code is shown by the boiler’s control board when it detects heating supply thermistor open or short circuit auto water supply. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| displays ‘205E’ on the front panel. If this occurs, the boiler shuts down. |
| Check the temperature displayed on the front panel. |
Common Causes
Causes documented in 2 technical sources.
| Cause |
|---|
| including leakage. |
| Faulty sensor |
Safety Warning
E205 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Identify which sensor is faulty from the error code (flow, return, DHW, flue gas, or outdoor)
Check the wiring — inspect the connections at both the sensor and the PCB for corrosion or loose terminals
Measure the sensor resistance with a multimeter — compare with the manufacturer's resistance/temperature chart (typically 10kΩ at 25°C (77 °F) for NTC sensors)
If resistance is out of range (infinite = open circuit, near zero = short circuit), replace the sensor
If resistance is correct, check the wiring continuity between the sensor and PCB
If wiring is good, test the PCB input
How to Fix It
Repressurise the system via the filling loop to 1.0-1.5 bar (15–22 psi)
repair any identified leaks
if the expansion vessel has lost its charge, re-pressurise it with a pump (or replace if the diaphragm has failed)
replace the pressure relief valve if it is passing water
replace the pressure sensor if it is giving incorrect readings. Note: frequent pressure loss indicates an underlying leak that must be found and repaired
Replace the defective heat exchanger output temperature sensor.
Refer to the Navien service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Navien models that can display fault code E205:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Navien models | — | Possible |
Frequently Asked Questions
Repressurise the system via the filling loop to 1.0-1.5 bar (15–22 psi). According to the technical documentation, this is the first check on the list for E205.
E205 is not classified as a high-severity fault, so the boiler can be reset once. If E205 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.