No LED light on the Tappan control board; furnace completely dead; blower and inducer do not run.

Safety: Use caution when working around live electrical circuits. Turn off power at the breaker before opening junction boxes.

Steps:

• Check the furnace service switch (usually mounted on or near the furnace) and ensure it is ON.
• Check the dedicated furnace circuit breaker in the electrical panel. Reset if tripped; if it trips again, there is a short that must be located.
• Remove the blower door and inspect the control board. Look for a small automotive-style fuse (3–5A). If blown, replace with the same rating. If it blows again immediately, there is a short in the 24V circuit (often thermostat wiring).
• Test the transformer primary for 120 VAC and secondary for 24 VAC. Replace the transformer if the primary has power but the secondary has no output.