Navien NPE-2 Code E593
Front panel key fault. A button on the front panel is reporting as stuck or shorted. It is the most mundane fault in the table, and the most likely to be something physical: a key held down, moisture, or a damaged panel. Navien's instruction is to contact technical support.
Part replacementThe verdict
Replace a part
Not a combustion fault and not urgent, but the heater will not take commands reliably until it is fixed. The panel is a moderate part, and moisture is worth ruling out first — if water is reaching the front panel, that is the real problem.
Typical cost: $150–$500
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NPE-2 — not averaged across the brand.
Source: Navien NPE-2 User's Information Manual (p. 17), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Check nothing is pressing against the front panel and that no button is visibly stuck.
- Look for any sign of moisture or condensation on or around the panel.
- Contact your installer or Navien technical support.
Frequently asked questions
Can I use the unit while E593 is showing?
That depends on which key is stuck and whether the heater will still respond to the controller. Even if it runs, get it fixed — a stuck key can put the unit into a mode you did not choose.
Code E593 on other Navien series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: