Noritz · Water heater
Code 20 High limit switch triggered
What this code means
An internal safety switch cut power because temperature exceeded its safe threshold.
Most likely causes
- Same root causes as Code 16: scale buildup or restricted flow
- Failing high-limit switch itself
What to try first
Power-cycle once; if it recurs, this needs professional diagnosis of the heat exchanger and flow.
Safety note: if this code returns after one clean reset, stop resetting it — repeated lockouts usually mean a real fault that needs a licensed technician. Never bypass a safety switch.
FAQ
What does Noritz error code Code 20 mean?
High limit switch triggered. An internal safety switch cut power because temperature exceeded its safe threshold.
Can I fix Noritz code Code 20 myself?
Usually not. Power-cycle once; if it recurs, this needs professional diagnosis of the heat exchanger and flow. If the code returns after one reset, it needs a licensed technician.
What causes Noritz code Code 20?
The most common causes are: same root causes as code 16: scale buildup or restricted flow; failing high-limit switch itself.
Other Noritz water heater codes
All Noritz water heater error codes →
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This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.