Navien · Tankless Water Heater Serious
E046 — Abnormality in Limit Control (Heat-Exchanger High-Limit)
Per the Navien NPE-series manual, E046 means an abnormality in the limit control — the heat-exchanger high-limit safety circuit has tripped or is reading incorrectly.
- Keep using it?
- Limited use only
- DIY difficulty
- Hard
- Verified against
- navieninc.com ↗
How to fix it
- Power off the unit and allow it to cool.
- Check for restricted water flow (closed valves, clogged inlet filter) that could cause the heat exchanger to overheat.
- If hard water is present, descaling the heat exchanger per Navien's manual may be needed.
- This is a safety-circuit fault — have a qualified technician verify the high-limit switch/sensor before returning the unit to service.
Why it happens
Typical signs: E046 on display · Unit locks out and will not fire · Possible overheat condition at the heat exchanger
- Heat-exchanger high-limit switch tripped A genuine overheat event (often from scale buildup restricting water flow through the heat exchanger) can trip this safety limit.
- Failed high-limit switch or sensor The limit-control device itself can fail and report a fault without an actual overheat.
- Restricted water flow through the heat exchanger Scale buildup or a flow restriction can cause the heat exchanger to run hotter than expected.
Parts you may need
If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.
- Navien heat-exchanger high-limit switch Common replacementAmazon →
More Navien tankless water heater codes
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: navieninc.com.