Honeywell TH8321WF1001 VisionPRO 8000 Wi-Fi Programmable Touchscreen Thermostat BLOWN-FUSE Error Fix: HVAC Control Board Fuse Blown

Error code BLOWN-FUSE on the Honeywell TH8321WF1001 VisionPRO 8000 Wi-Fi Programmable Touchscreen Thermostat means: HVAC Control Board Fuse Blown. The HVAC system is not responding because the low-voltage fuse (typically 3A or 5A automotive-style blade fuse) on the furnace or air handler control board has blown — this is most commonly caused by a wiring short during thermostat installation (crossing R and C wires), an incorrect wire connected to the wrong terminal, or a failing contactor in the outdoor unit; replace the fuse and verify all thermostat wiring before restoring power

The most successful fix is "Diagnose and Repair Wiring or Contactor Causing Fuse to Blow" (medium difficulty, ~75 minutes). Estimated DIY cost: $10-$25. HomeMD has 2 community-ranked fixes for this error.

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Yes — the top-ranked community fix ("Diagnose and Repair Wiring or Contactor Causing Fuse to Blow") is rated medium difficulty and takes about 75 minutes. Tools needed: Multimeter, Needle-nose pliers, Phillips screwdriver, Voltage tester.

DIY cost: $10-$25. Professional repair typically costs $200-$350. Many homeowners save money by trying the top-ranked community fix first.

The Honeywell TH8321WF1001 VisionPRO 8000 Wi-Fi Programmable Touchscreen Thermostat has 8 other known error codes, including: APP-OFFLINE (Thermostat Shows Offline in App), AUX-HEAT ("Aux Heat" Displayed), BLANK-SCREEN (Blank/Dead Display — No Power), COOL-ON-FLASH ("Cool On" Flashing on Display), EM-HEAT ("Em Heat" or Emergency Heat Mode), and 3 more.

Error code BLOWN-FUSE also appears on 7 other Honeywell models: RTH7600D 7-Day Programmable Thermostat with Backlit Display, RTH9585WF Wi-Fi Color Touchscreen 7-Day Programmable Thermostat, T10 Pro Smart Thermostat with RedLINK Room Sensor, T6 Pro Programmable Thermostat (TH6320WF / TH6220U), T9 Smart Thermostat with Smart Room Sensor, TH4210U2002 PRO 4000 5-2 Day Programmable Thermostat, and 1 more. The fix may vary by model, so check each model's specific page for tailored repair steps.