Burners ignite but shut off quickly; LED status light flashes four times repeatedly.

Safety first: Turn off power before servicing. The high limit switch protects against overheating; do not bypass it for operation.

Step-by-step checks:

• 1. Replace or clean air filter: Locate the filter in the return air duct or blower compartment. If dirty or clogged, replace with the correct size and airflow rating recommended for your Philco furnace.
• 2. Check supply and return vents: Walk through the home and open all supply registers and return grilles. Remove rugs or furniture blocking airflow.
• 3. Inspect blower wheel and motor: Remove the blower compartment door. Check the blower wheel for heavy dust buildup that can reduce airflow. Clean with a soft brush and vacuum (power off). Spin the wheel by hand; it should move freely. If stiff or noisy, the blower motor bearings may be failing.
• 4. Verify blower speed tap (if accessible): On some Philco models, the blower speed for heat is set via wires on the control board. Ensure the heat speed is not set too low for your duct system (this is best adjusted by a technician).
• 5. Inspect high limit switch: Locate the high limit (usually mounted on the heat exchanger panel). Check for loose wires or signs of overheating. After the furnace cools, the switch should reset automatically. If it trips repeatedly despite good airflow, it may be weak.

When to call a professional: Persistent high limit trips can indicate undersized ductwork, a cracked heat exchanger, or a failing blower. Have a licensed technician evaluate and replace the high limit switch with a Philco-approved part if needed.