Rinnai code 14 (overheat or thermal fuse): what to check

Rinnai display

14

“Heat Exchanger Overheat”

RU/RUR/RSC, RX, RE/REP, V, RL/VC · SENSEI RU Installation and Operation Manual, p. 73; SENSEI RUR Installation and Operation Manual, p. 72; SENSEI RSC Installation and Operation Manual, p. 72; SENSEI RX/CX Tech Sheet, p. 1; RE Series Installation and Operation Manual, p. 50; REP Series Installation and Operation Manual, p. 49; Value Series Installation and Operation Manual, p. 34; V53De Installation and Operation Manual, p. 29; VC Series Installation and Operation Manual, p. 37; Troubleshooting Tankless Water Heater Diagnostic Codes, p. 23–25
Owner checks, then technician

RE/REP tables: "Thermal Fuse" (RE manual, p. 50). Value, V53De and VC tables: "Thermal Fuse has activated" (Value manual, p. 34).

What it means

Code 14 is an overheat shutdown. The RU, RUR, RSC and RX tables tie it to the heat exchanger; the RE, REP, Value, V53De and VC tables tie it to a thermal fuse RU manual, p. 73; RE manual, p. 50; Value manual, p. 34. Rinnai’s troubleshooting guide says the code is a sign of overheating and should be taken seriously p. 23.

What trips it depends on the series. On SENSEI and RX models, an overheat sensor on the heat exchanger sets the code and resets itself once the heat exchanger cools; if the cause is not corrected, it keeps tripping troubleshooting guide, p. 23. On Non-SENSEI models two kinds of part can set it: a bi-metal switch that usually resets after cooling, and thermal fuses wrapped around the heat exchanger. The fuses are one-shot parts. A blown fuse must be replaced, which means removing the heat exchanger p. 24.

Scale is one of the causes the tables name: hot spots on the heat exchanger surface indicate blockage from scale build-up, and the remedy points to the flushing instructions RU manual, p. 73.

Check these first

Rinnai’s tables warn that consumers should never attempt any action they are not qualified to perform RU manual, p. 73; Value manual, p. 34. The V53De manual adds: call a licensed professional for any remedy that involves gas or electricity, or if you have any doubt about doing it yourself V53De manual, p. 28. If you smell gas, the Value and V53De manuals put one step before those in the box above: leave the premises Value manual, p. 28; V53De manual, p. 22.

1. If the heater is overheating or the gas does not shut off, turn off the manual gas control valve to the heater, by hand only RU manual, p. 8; Value manual, p. 3.
2. Check for anything restricting air flow around the heater and the vent terminal Value manual, p. 34; RE manual, p. 50; VC manual, p. 37. On the outdoor V53De, check around the unit and its exhaust outlet V53De manual, p. 29.
3. Look at the code history to see how often 14 has appeared. Turn the heater off with On/Off, hold On/Off for 2 seconds, then press Up; the last nine codes flash in turn RU manual, p. 73.
4. If 14 keeps coming back, stop and call for service. The troubleshooting guide says the overheat switch will keep tripping until the root cause is corrected pp. 23–24.

When to call a licensed technician

• Flushing the heat exchanger and treating hard water, which the tables name for scale RU manual, p. 73. The flush is section 6.3 of the RU manual p. 80; for RU, RUR and RSC models, Rinnai’s bulletin TB-188 Optimized Flushing Procedure for SENSEI Tankless Water Heaters revises it p. 1. Rinnai says repairs and maintenance shall be performed by a trained and qualified professional RU manual, p. 76. The Rinnai LC page summarizes what the flush involves.
• Measuring the overheat switch or the safety circuit RU manual, p. 73; Value manual, p. 34.
• Gas type, gas conversion, and high and low fire manifold pressure Value manual, p. 34; RE manual, p. 50.
• Low water flow in a circulating system that causes short-cycling Value manual, p. 34.
• Foreign material in the combustion chamber or exhaust piping, and cracks or separations in the heat exchanger Value manual, p. 34.
• DIP switch and parameter settings, including the forced Hi setting on RU, RUR and RSC models RU manual, p. 73; Value manual, p. 34.

Notes for different models

The air flow check in step 2 comes from the RE, REP, Value, V53De and VC tables. The RU, RUR, RSC and RX tables list only a switch measurement, the scale and flushing items, and the forced Hi setting RU manual, p. 73; SENSEI RX/CX Tech Sheet, p. 1.

On Value models, the technician also confirms that SW 5 in DIP switch bank 2 is off Value manual, p. 34. The VC manual describes the same check as switch 5 in the second (white) bank VC manual, p. 37.

Related Rinnai codes

• 16 “High Outgoing Temperature (safety shutdown because water heater is too hot)”
• 54 “High Exhaust Gas Temperature”
• LC “Scale Build-up in Heat Exchanger (when checking maintenance code history, “00” is substituted for “LC”)”
• SS “Service Soon (Flush Heat Exchanger)”

All Rinnai codes

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