Navien NPE-2 Code E788
Gas type setting does not match the panel. The gas type set on the panel DIP switches disagrees with the panel itself. Unlike most codes in this table, Navien gives a specific action: check the supplied gas type and match the gas type setting on the panel DIP switches and the panel. This code exists on the NPE-2 only.
Call a proThe verdict
Call a licensed plumber
A configuration disagreement about which fuel the heater is running on — which is not a setting to guess at. If the unit was recently installed, converted, or had a board or panel replaced, call that installer back: this code is pointing at their work, and correcting it is usually quick.
Typical cost: $0–$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-2 — not averaged across the brand.
Source: Navien NPE-2 User's Information Manual (p. 18), 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.
- Establish what your house actually runs on: natural gas from a meter, or propane from a tank.
- If the unit was installed, converted, or serviced recently, contact whoever did that work.
- Do not open the cabinet to change any switch settings yourself.
Frequently asked questions
Is the heater unsafe with this code showing?
It has stopped rather than run on a setting it cannot confirm, which is the safe behaviour. Do not work around it — the setting in question determines how much gas the burner gets.