What does Rinnai error code 14 mean?

Rinnai titles code 14 Thermal Fuse or Overheat Sensor. Two different safety parts can set it off, and they behave differently:

• The overheat bi-metal switch. This is mounted on the heat exchanger. Rinnai says it resets on its own once the heat exchanger cools, and the heater then runs again. If the cause is not fixed, the switch trips again the next time that temperature range is exceeded.
• The thermal fuses. Rinnai says these are wrapped around the heat exchanger and are a one shot device. Once one blows, it has to be replaced, and that means removing the heat exchanger.

Here is why that matters to you. If your heater threw a code 14, went cold for a while, and then came back on by itself, the resettable switch probably did the work. That does not mean the problem went away. Rinnai's manual is direct that the switch will keep tripping until the root cause is corrected.

Rinnai's troubleshooting list runs from simple settings to hardware. In the order the manual gives them, these are the main suspects:

• A DIP switch in the wrong position. On the models Rinnai lists, a certain switch on the circuit board de-energizes the gas valve circuit. Rinnai says if it is in the wrong position, the heater shows code 14. This is an installer or service item, not a homeowner switch.
• The wrong gas type. The heater has to match the fuel on its rating plate. Rinnai has technicians confirm the gas type, the venturi installed in the gas valve, and the gas type setting on the controller. A heater converted from natural gas to propane, or the other way, has to be converted to the manufacturer's specification.
• Wrong altitude or model settings. The controller has parameters for altitude range, input rating and indoor or outdoor exhaust. Rinnai says each has to be set correctly for the install.
• Poor clearances. Rinnai has technicians verify the clearances around the heater and the vent terminals. A heater packed in a closet with stored items against it can trap heat.
• Damaged safety circuit wiring. A loose connector or broken wire in the overheat circuit can look like an overheat. Rinnai's steps include inspecting the harness and testing the circuit with a meter.
• Short cycling. Rinnai says a heater that keeps switching on and off can move heat into the copper heat exchanger and trip the bi-metal switch. Its example is a system with a control that calls for hot water in short bursts, with a low temperature difference.
• Debris or scale on the heat exchanger. Rinnai's manual says buildup between the copper fins inside the heat exchanger can lead to a code 14. It tells technicians to look for black discoloration on the copper where it meets the combustion box, which Rinnai says indicates a blockage or debris between the fins. If debris has caused the overheat, Rinnai's step is to replace the heat exchanger.
• Gas pressure and venting problems. The manual has technicians check low and high fire manifold gas pressure with a manometer, and verify vent lengths and clearances.

If none of that turns up a cause, Rinnai's last step is to replace the circuit board.

Not much of that list is homeowner work, and Rinnai says as much. Its manual warns that you must be qualified to service gas systems, and that the electrical, gas and water supply should be off before anyone works on the heater. Still, a few things cost nothing and give a technician useful information.

Start with the gas smell rule, which comes before everything else. If you smell gas, do not touch a switch, do not use a phone inside, and leave. Call from outside. Southwest Gas takes emergency calls at 877-860-6020, and 911 works for any suspected leak.

If there is no smell:

1. 1Look at the space. Is anything stored against the heater, or blocking the area around it or the vent terminal? Move stored items away. Never store paint, solvents or aerosols near a gas appliance.
2. 2Let it cool and try again once. Turn the heater off at the controller, wait a few minutes, and turn it back on. If a code 14 comes back within hours or days, stop resetting it.
3. 3Read the code history. Rinnai's manual describes how to view the last nine codes from the controller: turn the heater off with the On/Off button, then press and hold On/Off for two seconds together with the Up button. Write the codes down. A run of 14, 14, 10 tells a technician something different from a lone 14. Hold the same two buttons to exit.
4. 4Note what changed. A code 14 that began after a new appliance on the gas line, a vent repair, a remodel around the heater or a stretch of many short hot water draws points the technician toward the cause.

Do not open the cabinet, and never bypass or jumper a safety device. These parts are there to protect the house.

The visit follows Rinnai's list, with instruments. A technician checks the settings on the controller and the circuit board against the model and the install. They confirm the gas type and the gas valve venturi, verify clearances and vent lengths, and measure the resistance of the overheat circuit to tell an open bi-metal switch from a blown thermal fuse.

They also look at the heat exchanger. Rinnai has them inspect the front, sides and back for cracks, separations, discoloration or damage, and look between the copper fins for buildup. They check for short cycling in the plumbing system. If a thermal fuse has blown, the heat exchanger comes out, and every item on the list is inspected before it goes back in.

### Why hard water matters here

Phoenix has hard water, and a heat exchanger that is scaled up has to work harder to move heat into the water. Rinnai's manual includes flushing the heat exchanger as one of its steps for code 14, and it points to the flushing procedure in the owner's manual. Scale is not the only cause of a code 14, but a heater that has never been flushed is more likely to have several small problems at once. Our page on how often to descale a tankless water heater in Phoenix covers the schedule, and our page on Rinnai code LC explains the scale warning the heater gives before it comes to this.

Call the first time a code 14 returns after a reset. A resettable overheat switch that trips more than once is telling you something is wrong, and a blown thermal fuse means the heater will not run at all until a technician replaces it. Also call for any code 14 that appears alongside a burnt smell, discoloration on the cabinet, or a heater that is too hot to touch.

HQ Plumbing and Air is licensed and insured, and answers emergency calls 24/7. Your estimate is free and the price is quoted before work starts. When the heater is old and the repair list is long, our page on whether to repair or replace a water heater can help you decide.

If your Rinnai is showing a different code, see our pages on Rinnai error code 10 for air and exhaust trouble, Rinnai error code 11 for no ignition, and Rinnai error code 12 for flame failure.