Water heater shuts down and displays Code 05; unit may feel very hot to the touch around the heat exchanger area
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Turn OFF gas and power. Do not operate the heater with a known venting blockage; risk of carbon monoxide exposure.
Steps to check:
- Inspect outdoor vent terminals: Check both intake and exhaust terminals for leaves, snow, bird/insect nests, or other obstructions. Clear any debris.
- Check vent piping: Visually inspect accessible vent sections for disconnections, sags, or crushing. Ensure proper slope and support per Rinnai installation manual.
- Clean air filter: Many Rinnai models have an intake air filter behind the front cover. Remove and clean it with mild soap and water, dry thoroughly, and reinstall.
- Reset and test: Restore gas and power, reset the unit, and run hot water. If Code 05 returns quickly, internal overheat or vent design issues may exist.
When to call a professional: Persistent Code 05 after clearing vents may indicate a scaled heat exchanger or improper vent sizing. A technician should descale the heat exchanger and verify vent design.
Repair Difficulty
Required Part
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