E594 — Control Board EEPROM Error
The control board's EEPROM (its memory chip) is behaving abnormally — a memory read/write fault on the PCB. This is not a gas valve or modulation problem.
- Keep using it?
- Limited use only
- DIY difficulty
- Moderate
- Verified against
- navieninc.com ↗
How to fix it
- Power-cycle the unit (off at least 60 seconds) and see if the code clears.
- If the code returns, this is a control-board-level fault, not something to diagnose with a multimeter at the flame rod or gas valve.
- Contact Navien technical support or a licensed technician for control board diagnosis, reset, or replacement.
Why it happens
Typical signs: E594 displayed · Unit inoperative or locked out · Settings or programming may not save correctly
- Memory chip fault on the PCB The EEPROM that stores unit settings and calibration data is failing to read or write correctly.
- Power surge or brownout A voltage spike or sudden power loss during a write cycle can corrupt EEPROM data.
- PCB defect A manufacturing or component-level fault on the control board itself.
More Navien tankless water heater codes
Frequently asked questions
What does the E594 code mean on a Navien tankless water heater?
The control board's EEPROM (its memory chip) is behaving abnormally — a memory read/write fault on the PCB. This is not a gas valve or modulation problem.
What causes the E594 code on a Navien tankless water heater?
Memory chip fault on the PCB: The EEPROM that stores unit settings and calibration data is failing to read or write correctly. Power surge or brownout: A voltage spike or sudden power loss during a write cycle can corrupt EEPROM data. PCB defect: A manufacturing or component-level fault on the control board itself.
Is it safe to keep using a Navien tankless water heater with a E594 error?
Limited use only. This is rated a serious-severity fault.
How do I fix E594 on a Navien tankless water heater?
Power-cycle the unit (off at least 60 seconds) and see if the code clears. If the code returns, this is a control-board-level fault, not something to diagnose with a multimeter at the flame rod or gas valve. Contact Navien technical support or a licensed technician for control board diagnosis, reset, or replacement.
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: navieninc.com.