Navien NPE-A / NPE-S Code E593
Front panel key fault. A fault in the front panel keypad — a button reading as stuck or the panel not responding correctly. The unit is reporting its own controls, not the water side.
Part replacementThe verdict
Replace a part
A control panel fault. Not urgent in the way a combustion code is, but it will keep the unit from being set properly.
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-A / NPE-S — not averaged across the brand.
Source: Navien NPE Operation Manual (NPE-A / NPE-S) (p. 16), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Check for anything pressing against the panel, and for water or condensation on it.
- Book a service call.
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: