Rheem R802VA07542117MSA Error Code A031_F: Open Fuse
What Does Code A031_F Mean?
Fault code A031_F on the Rheem R802VA means the low-voltage fuse protecting the 24VAC circuit on the IFC board has opened (blown). The IFC reports fault code 30 via Bluetooth when this fuse has been opened. With this fuse blown, the control board, thermostat, and all 24VAC accessories lose power and the furnace cannot operate.
The 24VAC fuse protects the circuit from short circuits between the 24VAC hot leg and the Ground or Common (C) wire. The most common cause is thermostat wiring where two wires have shorted together — for example, where wire insulation has worn away at a nail or staple, or where a wire terminal has been incorrectly connected. A defective thermostat or an accessory such as a zone controller, humidifier, or UV light can also cause the short.
Simply replacing the fuse without finding and correcting the short will cause the new fuse to blow immediately or shortly after. A technician must systematically isolate the 24VAC circuit — disconnecting the thermostat wires at the board and each accessory — to locate the fault before installing a new fuse.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- Any time this code appears — a technician must locate the short circuit before replacing the fuse, otherwise the replacement fuse will blow again
- If the new fuse blows immediately after installation, the short circuit is still present and requires further diagnosis
- A technician should trace all 24VAC wiring including runs inside walls where damage may not be visible
✓ Verified against manufacturer service manual — March 2026