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
Other Navien series report code E593 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Navien NPE-A / NPE-S code points at the control panel too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: