Navien NPE-2 Code E016
Overheating of heat exchanger. The heat exchanger got hotter than it should. Navien's two remedies point straight at what usually causes it: clean the cold water inlet filter, and flush the heat exchanger. Both are about water flow — if water cannot move through the exchanger freely, or scale is insulating the metal, the heat has nowhere to go.
Call a proThe verdict
Call a licensed plumber
Do not keep resetting it. Navien's own answer is a filter clean and a flush, and on a unit that has never been descaled that is very likely the fix — but an overheat on a gas appliance deserves eyes on the heat exchanger too, because if it has already been cooked, flushing does not undo that.
Typical cost: $150–$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-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
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Turn the unit off and leave it off until it has been checked.
- Note when it was last flushed and whether your water is hard — Navien names the flush as a remedy for this code.
- Clean the cold water inlet filter, which is Navien's other listed step and is a ten-minute job.
- Book a licensed professional if the code returns after that.
Frequently asked questions
The original NPE manual says to turn the system off for 30 minutes and restart. Should I?
That instruction is in the first-generation NPE manual for this code; Navien dropped it from the NPE-2 manual, which lists only the filter clean and the flush. Waiting for it to cool lets it run again — it does not fix what made it overheat.
Is this the same as E030?
No. E016 is the heat exchanger overheating; E030 is the exhaust overheating, measured at the flue. They share scale as a root cause and share Navien's remedies, but they are different sensors reporting different things.
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: