Navien NPE-A / NPE-S Code E047
Exhaust thermostat fault. The exhaust thermostat is not behaving. This generation words it as an abnormal operation of the exhaust thermostat; the NPE-2 manual narrows the same code to the thermistor being open or short circuit. Either way it is the device that watches flue temperature, and Navien's instruction to the owner is to contact technical support.
Call a proThe verdict
Call a licensed plumber
A sensor in the exhaust path. Modest part, but it sits in the combustion side of the unit and Navien does not offer an owner step.
Typical cost: $150–$600
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.
- Book a licensed professional — the manual gives no owner-side check for this code.
Code E047 on other Navien series
Code E047 is a different fault on every other Navien series that documents it, which is exactly why this page is written for the NPE-A / NPE-S alone:
Don't confuse this with
One other Navien NPE-A / NPE-S code points at the exhaust path 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: