Furnace does not respond to thermostat; LED shows code 11 (no previous code / no fault stored) but no heat.

Safety: Turn off furnace power before accessing the control compartment.

Steps:

• Check thermostat settings: Ensure the thermostat is set to HEAT and the setpoint is above room temperature. Replace thermostat batteries if applicable.
• Inspect low-voltage fuse: Open the blower door and locate the 3–5A automotive-style fuse on the Keeprite control board. If blown, replace with the same rating. If it blows again, there is a short in the low-voltage wiring.
• Verify thermostat wiring: Confirm that the W (heat) wire is securely connected at both the thermostat and the furnace control board. Look for damaged or pinched thermostat cable along its run.
• Test for 24V call: With a multimeter, measure between R and C (should be ~24VAC). Then measure between W and C when there is a call for heat. If no voltage appears at W, the thermostat or wiring is faulty.

Call a technician if the control board has proper 24V input and a valid call for heat but does not start the ignition sequence; the board may need replacement.