Rinnai 14
Rinnai code 14: overheat safety, causes and fixes
Short answer
Code 14 means an overheat safety in the Rinnai tripped because part of the unit got too hot. Rinnai uses two devices for this: a bi-metal switch that resets itself once it cools, and thermal fuses that must be replaced once they blow. Either way, the cause of the overheating has to be found.
In this guide
Code 14 is one of the more serious codes on a Rinnai tankless water heater. Rinnai's own troubleshooting guide describes it as a sign of overheating that should be taken seriously.
The unit uses two kinds of overheat protection, and which one tripped decides what happens next.
Do not bypass or jumper an overheat switch or thermal fuse. They exist to prevent overheating and fire.
Bi-metal switch vs thermal fuse
| Device | What happens |
|---|---|
| Bi-metal overheat switch | Mounted on the heat exchanger. It usually resets on its own once the unit cools, and the heater runs again. If the cause is not fixed, it trips again. |
| Thermal fuses | Wrapped around the heat exchanger on some models. They are one-time devices and must be replaced once blown, which means removing the heat exchanger. |
So if code 14 cleared after the unit cooled down, the switch reset itself, but the unit still ran too hot for a reason. If it will not clear at all, a fuse may have blown.
What you can check yourself
- Look at the outside vent terminal and clear any snow, ice, leaves or debris.
- Check for disconnected or damaged vent pipe where it is visible.
- Think about maintenance. If the unit has not been descaled in more than a year, especially with hard water, scale is a strong suspect.
- Make sure nothing is stored against the heater that blocks air around it.
Common causes of Rinnai code 14
Scale or debris in the heat exchanger
Scale on the water side and debris between the fins on the combustion side both keep heat from moving into the water. The metal overheats instead. Rinnai's procedure includes flushing the heat exchanger and inspecting the fins.
Wrong gas type or gas pressure
A unit connected to the wrong gas type, converted incorrectly, or running with gas pressures out of range can overfire and overheat.
Venting and clearances
Blocked vents or a vent terminal installed too close to walls or other vents can let hot exhaust recirculate.
Short cycling
In some recirculation setups, the heater turns on and off very frequently. Heat builds up in the heat exchanger and can trip the switch.
Wiring, settings or the control board
Damaged overheat circuit wiring, an incorrect setting or DIP switch, or a failing control board can also show code 14.
Why this code needs a technician
Finding the cause means checking gas pressures with a manometer, inspecting the burner and heat exchanger, and testing the safety circuit. Rinnai limits these steps to trained professionals. Look for discoloration on the heat exchanger too: a blackened area where the copper meets the combustion box points to blocked fins and usually means the heat exchanger has to be replaced.
How to prevent it
Descale the unit once a year, or more often with hard water, keep the vent terminal clear and have the unit serviced if other codes start appearing.
Common questions
Can I reset Rinnai code 14 myself?
If the bi-metal switch tripped, the unit may run again once it cools. That does not fix the cause, so the code will likely return. If a thermal fuse blew, the unit will not reset until the fuse is replaced.
Does hard water cause Rinnai code 14?
It can. Scale builds up in the heat exchanger and makes it run hotter, which is one of the common causes of this code.
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Other Rinnai codes
| Code | Meaning |
|---|---|
| 02 | No burner operation during freeze protection |
| 03 | Power interruption during bath fill |
| 05 | Bypass flow control device fault |
| 10 | Air supply, exhaust blockage or condensate trap full |
| 11 | No ignition |
| 12 | Flame failure |
| 14 | Thermal fuse or overheat sensor tripped |
| 15 | Venturi control fault |
| 16 | Outgoing water temperature too high (safety shutdown) |
| 17 | Venturi blockage |
| 19 | Electrical grounding fault |
| 21 | Data transfer error after a control board replacement |
| 25 | Condensate drain clogged or condensate pump error |
| 32 | Outgoing water temperature sensor (thermistor) fault |
| 33 | Heat exchanger temperature sensor (thermistor) fault |
| 34 | Combustion air temperature sensor fault |
| 38 | Exhaust gas temperature sensor fault |
| 41 | Freeze protection sensor fault |
| 51 | Inlet water temperature sensor fault |
| 52 | Gas valve or modulating solenoid valve signal fault |
| 54 | High exhaust gas temperature |
| 57 | Burner overheat switch open |
| 58 | Secondary heat exchanger overheat |
| 61 | Combustion fan motor fault |
| 63 | Recirculation low flow |
| 65 | Water flow control device (servo) fault |
| 70 | Control board (PC board) fault |
| 71 | Gas solenoid valve circuit fault |
| 72 | Flame rod (flame sensing) fault |
| 73 | Burner thermocouple fault |
| 79 | Water leak detected inside the unit |
| LC | Scale buildup in the heat exchanger |
| SS | Service soon (maintenance reminder) |
| FF | Maintenance has been performed (service history marker) |