Furnace displays F7, will not start, thermostat appears to call for heat but no response

Safety: Turn off power to the furnace before accessing the control compartment. Low-voltage circuits can still be damaged by shorts.

Steps:

• Check thermostat settings: Ensure the thermostat is set to HEAT and the setpoint is above room temperature. Replace batteries if applicable.
• Inspect low-voltage fuse: Remove the blower door and locate the Ideal control board. Look for a small automotive-style fuse (often 3–5 A). If blown, replace with the same rating only. If it blows again, there is a short that needs professional diagnosis.
• Check thermostat wiring: Confirm that the R, W, Y, G, and C wires (as used) are firmly connected at both the thermostat and the furnace control board, with no bare copper touching.
• Bypass test (for qualified persons only): With power off, temporarily connect R and W at the control board, then restore power. If the furnace starts normally, the thermostat or its cable is likely faulty and should be replaced.