54 High exhaust gas temperature

What the control is telling you

Exhaust temperature rose above 163°F. The unit first reduces its firing rate; if the exhaust is still above 163°F after 120 seconds it shuts down and displays 54.

Applies to: SENSEI Series, SENSEI RX/CX Series, Non-SENSEI Series

Likely causes

• Vent termination clearances not met
• Blocked intake or exhaust ports / vent over allowed length
• Unit running on a gas type that does not match the rating plate
• Inlet water temperature above 160°F
• Scale build-up or debris in the heat exchanger
• Faulty exhaust gas temperature sensor or wiring
• Air leaking from the fan into the combustion chamber
• Faulty PC board

Test and repair steps

1. Confirm the vent termination meets the required clearances.
2. Look for blockages at the intake and exhaust ports of the vent system.
3. Verify vent length and clearances comply with Rinnai's installation specifications.
4. Confirm the gas supplied matches the gas type on the rating plate.
5. Make sure incoming water temperature does not exceed 160°F.
6. Warning: Turn off electrical, gas and water supply to the heater before continuing.
7. Check the heat exchanger for hot spots (sign of internal scale). Flush with four gallons of vinegar per the owner's manual; replace the HX if neglect has damaged it; treat the water if scale caused the code.
8. Inspect the exhaust gas temperature sensor, wiring and PC board connections and measure circuit resistance (e.g., 11.4–14K ohms at 59°F, 2.2–2.7K at 140°F). Compare against the full list in the source manual (p.49).
9. Check for fan air leakage between the air intake and the combustion chamber.
10. SENSEI / SENSEI RX/CX Remove the heat exchanger, separate the burner from the primary HX, inspect the fins and blow out any debris with 120 psi compressed air.
11. SENSEI / SENSEI RX/CX A removed burner gasket must never be reused; install a new 101 Burner Gasket-Large and make sure burner plate and HX surface are clean and smooth.
12. Non-SENSEI Remove the manifold, sight plate and burner assembly to inspect the HX fins; clean debris with 120 psi compressed air and replace damaged gaskets.
13. If code 54 persists after these checks, replace the PC board.

Settings for these units

RSC supply connection sizes · SENSEI

The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.

Condensate drain line must stay at least 1/2 in. over its whole length.

RSC water quality limits · SENSEI

Damage from water above these limits is not covered by warranty.

Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.

• RSC clearances to combustibles · SENSEI
• RSC temperature settings available · SENSEI
• RX supply connection sizes · SENSEI RX/CX
• RX water quality limits · SENSEI RX/CX
• RX water treatment and flushing by hardness · SENSEI RX/CX
• RX clearances to combustibles · SENSEI RX/CX

Models that show this code

89 models in Non-SENSEI, RH180 hybrid, SENSEI RX/CX, SENSEI

Other codes on the same units

• 38 Exhaust gas temperature sensor (CO sensor on RH180)
• 41 Freeze protection / outdoor air temperature sensor fault
• 51 Inlet water temperature thermistor fault
• 52 Gas valve / modulating solenoid valve (POV) signal fault
• 57 Burner overheat bi-metal switch open
• 58 Secondary heat exchanger bi-metal switch open
• 61 Combustion fan motor fault
• 63 Recirculation low flow