On the covered Rinnai tankless water heater, 54 means high exhaust gas temperature. First, check that the condensate line is not blocked or frozen, then reset the water heater's power once. Then: Rinnai's checks: the condensate line is not blocked, the heat exchanger fins are clean and not blocked, and the inlet water temperature is not too high. Clear the code by resetting the main power supply to the water heater.
Try in this order
0 of 4 completedWhat to do first
ReversibleCheck that the condensate line is not blocked or frozen, then reset the water heater's power once.
Correct only the documented fault domain
ReversibleRinnai's checks: the condensate line is not blocked, the heat exchanger fins are clean and not blocked, and the inlet water temperature is not too high. Clear the code by resetting the main power supply to the water heater.
Flush the heat exchanger
ReversibleIf the exhaust temperature stays above 163 F for 120 seconds the heater cuts back and then shuts down with code 54. Scale inside the heat exchanger is a common cause; Rinnai's guidance is to flush it with vinegar as the owner's manual describes.
Check the inlet water temperature
ReversibleInlet water that is already hot raises the exhaust temperature too.
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Common questions about “Rinnai tankless water heater code 54”
What does 54 mean on a Rinnai tankless water heater?+
High exhaust gas temperature.
What temperature triggers Rinnai code 54?+
When exhaust gas stays above 163 F for 120 seconds the heater shuts down and flashes code 54, after first reducing its firing rate.