Ideal furnace locks out with F4, burner shuts down during operation, may cycle on and off frequently

Safety: Turn off power before removing panels. Components around the heat exchanger can be very hot; allow the furnace to cool.

Steps:

• Check and replace air filter: Locate the Ideal furnace return air filter (often in the return duct or blower compartment). If dirty or clogged, replace with the correct size and airflow rating.
• Open vents and registers: Ensure all supply and return grilles in the home are open and not blocked by furniture, rugs, or curtains.
• Inspect blower operation: With panels in place, restore power and call for heat. Confirm the main blower starts shortly after ignition and runs steadily. If it is slow, noisy, or stops intermittently, the blower motor or capacitor may be failing.
• Reset high limit (if manual reset type): With power off, locate the high limit thermostat on the heat exchanger panel. Some Ideal models have a small red reset button; press gently if present. If it trips repeatedly, do not continue to reset—find and fix the cause.
• If F4 persists: The high limit switch or blower assembly may need replacement and the heat exchanger should be inspected by a qualified technician.