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
Frequently asked questions
What does the E046 code mean on a Navien tankless water heater?
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.
What causes the E046 code on a Navien tankless water heater?
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.
Is it safe to keep using a Navien tankless water heater with a E046 error?
Limited use only. This is rated a serious-severity fault.
How do I fix E046 on a Navien tankless water heater?
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.
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.