Rheem 305, 505, 705 Error 34: Combustion Air Temperature Sensor Fault

Tankless water heater · taken from the manufacturer’s manual, pages cited

Fault code34

Combustion Air Temperature Sensor Fault occurs due to restricted airflow, damaged sensor wiring, or a loose fan blade. The manual's first action is: “Check sensor wiring for damage.”

Model
Rheem 305, 505, 705
Display shows
Combustion Air Temperature Sensor Fault (34)
Type
Fault code
Source
Manual p. 10

What 34 means

Combustion Air Temperature Sensor Fault p. 10

Common causes

  • Check for restrictions in air flow around unit and vent terminal. p. 10
  • Measure resistance of sensor. p. 10
  • Ensure fan blade is tight on motor shaft and is in good condition. p. 10

What to do

  1. Check sensor wiring for damage. p. 10
  2. Clean sensor of scale build-up. p. 10
  3. Replace sensor. p. 10

Before you service the product, read the safety instructions in the manual p. 4.

If 34 is still not resolved

  • Immediately call your gas supplier from a neighbor’s phone. p. 1
    “Immediately call your gas supp lier from a neighbor’s phone.”
  • If you cannot reach your gas supplier, call the fire department. p. 1
    “If you cannot reach your gas supplier, call the fire department.”
Open the manual at page 10 All 305, 505, 705 error codes Manual details & download

This page summarises what the manufacturer’s manual says about 34; each statement links to the page it comes from, and quoted lines are copied word for word. It is not a substitute for the manual or for a qualified installer. ManualLib is not affiliated with Rheem. Found a mistake? Report an error.