Navien NPE-A / NPE-S Code E016
Overheating of heat exchanger. The heat exchanger got hotter than it should and the unit shut down to protect itself. On this generation Navien gives owners three steps and the first one is the one the NPE-2 manual later dropped: turn the system off for at least 30 minutes and restart it. Then clean the cold water inlet filter, then flush the heat exchanger — which names the real cause, because restricted flow and scale are what make a heat exchanger overheat.
Call a proThe verdict
Call a licensed plumber
Navien's own remedy list here is free: wait, clean the inlet filter, flush the unit. That is why the bottom of this range is zero. But an overheat that comes back after a flush is a real fault, and the heat exchanger is the most expensive part on the heater.
Typical cost: $0–$1,400
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
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Turn the system off and leave it off for at least 30 minutes before restarting. This is Navien's first instruction on this generation.
- Clean the cold water inlet filter — a clogged filter starves the exchanger of flow, which is exactly how it overheats.
- Flush the heat exchanger if it has not been descaled recently.
- If the code returns after all three, stop and book a licensed professional rather than resetting again.
Frequently asked questions
Why does my NPE-2 manual not mention waiting 30 minutes?
Because Navien removed that step. The first-generation NPE manual opens the E016 remedy with turning the system off for at least 30 minutes; the NPE-2 manual lists only the inlet filter and the flush. If your unit is an NPE-240A rather than an NPE-240A2, the wait is part of the documented procedure.
Code E016 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: