Noritz 14
Noritz error code 14: thermal fuse blown
Short answer
Error code 14 means the heat exchanger overheated badly enough to blow the thermal fuse, a one-time safety device wrapped around the heat exchanger. Noritz says it cannot be reset: the fuse must be replaced, and because that takes about as much work as a heat exchanger swap, Noritz recommends replacing both. The most common cause is scale buildup.
Noritz units with a copper heat exchanger have a thermal fuse wrapped around all four sides of it. If the heat exchanger gets dangerously hot, the fuse physically breaks and shuts the heater down. Code 14 means that has happened.
The meaning below comes from Noritz's own technical knowledge base. Noritz technical support: 866-766-7489.
Noritz warns never to bypass the thermal fuse. It is a critical safety device that prevents further damage to the unit or the home.
Why it happens
According to Noritz, the most common cause is scale buildup. Hard water minerals coat the inside of the heat exchanger and act as insulation, so heat stays in the copper instead of moving into the water. The heat exchanger overheats and the fuse blows.
Repeated error code 20 (high limit switch) warnings that are reset without finding the cause often come before a code 14.
The repair
A blown thermal fuse cannot be reset. Replacing it means removing the heat exchanger, which Noritz says can take two to four hours depending on access. For that reason, Noritz recommends replacing the heat exchanger at the same time, since the old one has already been badly overheated.
Warranty
Scale damage is commonly excluded from tankless warranties. If the unit is still under warranty, ask your technician to document the cause, and keep records of past descaling.
Preventing a repeat
Descale the heat exchanger on schedule and treat hard water. Our guide to descale a tankless water heater covers the job.
Before you call
Have the model and serial number from the rating label ready, along with the exact code and when it appears: at startup, during use, or only at high demand. Mention any recent work on the gas, water or electrical supply and when the heater was last serviced. This helps the technician bring the right parts and often saves a second visit.
See every code on our Noritz error codes page.
Common questions
Can I reset Noritz error code 14?
No. The thermal fuse is a one-time part that physically breaks. It must be replaced.
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Other Noritz codes
| Code | Meaning |
|---|---|
| 10 | Combustion abnormality (warning) |
| 11 | Ignition failure |
| 12 | Flame loss |
| 13 | Optional CO alarm device fault |
| 14 | Thermal fuse blown (severe overheat) |
| 16 | Outlet water temperature spiked too high |
| 20 | High limit switch tripped |
| 29 | Condensate drain problem (condensing models) |
| 67 | Air gas mixer (AGM) abnormality |
| 71 | Gas valve circuit abnormality |
| 90 | Combustion abnormality |
| 92 | Neutralizer near end of life (first warning) |
| 93 | Neutralizer at end of life |