Furnace does not respond to thermostat; E7 code on control board

Safety: Turn off furnace power before touching control wiring.

• 1. Check 3–5A blade fuse: On many Frigidaire control boards, a small automotive-style fuse protects the 24V circuit. Inspect and replace if blown with the same rating. If it blows again, there is a short in the low-voltage wiring.
• 2. Inspect thermostat wiring: At the furnace control board, verify R, W, G, and Y wires are firmly attached and not shorted together. Look for bare copper touching the metal cabinet.
• 3. Bypass thermostat (test only): With power off, remove the W wire from the board. Restore power and briefly jumper R to W at the control board. If the furnace starts, the thermostat or its wiring is suspect. Remove the jumper after testing.
• 4. Check thermostat settings: Ensure the thermostat is set to HEAT mode and the setpoint is above room temperature. Replace batteries if applicable.
• 5. Professional help: If E7 persists with correct wiring and a known-good thermostat, the control board may have a low-voltage circuit fault and require replacement.