33
Richmond
Air Intake / Combustion Air Thermistor Fault
Richmond tankless heater shows error 33 and will not operate.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed intake air temperature sensor, Loose sensor wiring, Sensor shorted by moisture, Faulty control board input
How to Fix / Troubleshooting
Safety first: Turn OFF power and gas. Work carefully around intake and combustion components.
- Locate intake sensor: On sealed-combustion models, the intake air thermistor is mounted near the air inlet or on the combustion fan housing. Remove the front cover to access.
- Inspect wiring: Check the sensor connector and wiring harness for moisture, corrosion, or damage. Dry any moisture and reseat the connector.
- Test sensor: With power OFF, disconnect the sensor and measure resistance with a multimeter. Compare to Richmond's temperature/resistance chart. Replace if out of range.
- Check for water intrusion: Inspect the intake vent termination and piping for signs of rainwater entry. Correct any improper terminations or slopes.
- Board evaluation: If a new sensor does not clear error 33, the control board may be defective and should be replaced by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Intake Air Temperature Sensor
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