Navien tankless water heater code E593
Front panel key fault. Code E593 means the same thing on all 2 Navien series documented here — but the fix, and what it costs, is still worth reading for your exact unit.
What code E593 means on each Navien series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| NPE-2 | Front panel key fault | Part replacement | $150–$500 |
| NPE-A / NPE-S | Front panel key fault | Part replacement | $150–$500 |
Each row opens the full page for that generation. We hold manuals for NPE-2 and NPE-A / NPE-S, and each one gets its own reading of code E593 — what Navien documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 2 series in four columns, which is enough to route you and not enough to explain anything. This is the Navien wording behind each row, one entry per manual, so you can see where the 2 readings of code E593 agree and where they part company.
NPE-2 — 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.
NPE-A / NPE-S — 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.
Does it matter which Navien you have?
NPE-2 and NPE-A / NPE-S all route code E593 the same way: a replacement part, at $150–$500. That makes it one of the Navien numbers you can act on before working out which unit you own.
Which Navien do you have?
On the 2 series that report code E593, the model number on the rating label starts NPE — match yours against the 13 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Navien NPE-2 User's Information Manual (p. 17), read Aug 2026 — the manufacturer's own documentation for this Navien range.
Source: Navien NPE Operation Manual (NPE-A / NPE-S) (p. 16), read Aug 2026 — the manufacturer's own documentation for this Navien range.
Parts, guides and symptoms behind code E593
Code E593 on these 2 Navien series points at 2 parts, each named by the manufacturer's own procedure for this code.