Code 14 = Overheat / thermal fuse trip. A safety thermistor in the burner or heat-exchanger area detected temperature above safe limit and locked out the unit. Serious code — won't restart until underlying cause is addressed.
Almost always: scaled heat exchanger
By far the most common cause. Scale insulates the heat exchanger from water flow. Burner can't transfer heat fast enough; metal temperature rises until safety trips. Fix: full descale. Severe scaling can permanently damage the heat exchanger — $700-1,500 replacement.
Other causes
Restricted combustion air
Blocked intake (lint, debris) or undersized intake venting. Inspect and clean the air inlet filter.
Restricted exhaust
Bird nest, ice, undersized vent. Inspect exterior termination.
Low water flow during draw
If GPM drops below threshold mid-draw (clogged inlet screen, partially closed isolation valve), exchanger heats faster than water removes heat. Clean inlet water filter.
NRCB combi: heating loop issue
On combi units, if the heating-loop circulator pump fails or air-lock develops, hot water can't move away from the exchanger. Code 14 results. Verify heating circulator and purge air.
Reset procedure
- Power off completely
- Wait 30 minutes to cool
- Power back on, attempt Level 1 reset
- If code returns immediately, do NOT keep resetting
If Code 14 persists
Stop troubleshooting DIY and call a Noritz-trained installer. Repeated overheat events cause cumulative heat-exchanger damage.
Prevention
- Annual descaling — non-negotiable in hard water
- Water softener above 11 grains per gallon
- Annual inlet filter cleaning
- Annual vent inspection
Bottom line
Code 14 is the cost of skipping annual maintenance. Descale, then call an installer if it returns. Don't cycle the reset — accelerates exchanger damage.