Furnace will not start at all; no blower, no inducer, no LED lights on Tempstar control board.

Safety: Use caution when working around 120V circuits. Turn off the breaker before removing covers.

• Step 1 – Check breaker and switch: Verify the furnace breaker in the electrical panel is ON. Locate the furnace service switch and ensure it is ON.
• Step 2 – Verify door switch: Remove and reinstall the blower door, ensuring it fully depresses the door safety switch. A misaligned door can cut power to the board.
• Step 3 – Test incoming power: With a multimeter and power ON, carefully measure voltage at the furnace line terminals (L1 and neutral). You should see ~120V. If not, there is an upstream electrical issue.
• Step 4 – Check transformer: With power off, inspect the Tempstar transformer for burns or loose wires. With power on, verify 120V on the primary and ~24V on the secondary. Replace the transformer if 24V is missing.