Ruud Combustion Air Temperature Sensor Fault

Ruud tankless water heater shows error code 34; unit may shut down or run at reduced capacity.

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.

Possible Causes

Failed combustion air thermistor, Loose or corroded connector, Damaged sensor wiring

Safety first: Turn OFF power and gas.

Step 1 – Locate combustion air sensor: Remove the front cover and find the air temperature sensor near the combustion air intake or blower.
Step 2 – Inspect and reseat: Check the connector and wiring for damage. Reseat the connector firmly.
Step 3 – Replace sensor: If the sensor is cracked, burnt, or tests out of spec, remove it and install a new OEM Ruud combustion air temperature sensor.

After replacement, restore power and test. Persistent error 34 may indicate a control board fault.

Medium 3/5

Combustion Air Temperature Sensor

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