Using the wrong gas Parameter RESET
The E773 error code on Navien boilers indicates using the wrong gas parameter reset.
Navien E773 means: using the wrong gas parameter reset. The usual causes are boiler has entered safety lockout due to a previous fault, safety device has tripped (overheat thermostat, flame failure) or transient fault that has cleared. You can safely reset the boiler once — if E773 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does E773 Mean
The E773 code is shown by the boiler’s control board when it detects using the wrong gas parameter reset. 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 |
|---|
| The display shows E773 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 2 technical sources.
| Cause |
|---|
| Boiler has entered safety lockout due to a previous fault |
| safety device has tripped (overheat thermostat, flame failure) |
| transient fault that has cleared |
Safety Warning
E773 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
Check for visible damage on the PCB — look for burnt components, corrosion, or water marks
Check all wiring connections to the PCB are secure
Try a power cycle — switch the boiler off at the mains for 30 seconds, then switch back on
If the fault persists after power cycling, check the error code history for related faults
Verify the mains voltage supply to the PCB is stable (230V ±10%)
Check the earth connection
How to Fix It
Power cycle the boiler (off for 30 seconds, then on)
repair loose connections
if the PCB shows signs of water damage or burnt components, replace the PCB
ensure the replacement PCB is the correct version for the boiler model
after PCB replacement, the boiler may need recommissioning and parameter setup
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 E773:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Navien models | — | Possible |
Frequently Asked Questions
Power cycle the boiler (off for 30 seconds, then on). According to the technical documentation, this is the first check on the list for E773.
E773 is not classified as a high-severity fault, so the boiler can be reset once. If E773 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.