LED flashes code 45; furnace locks out and may require power cycling to restart.

Safety: Turn off power before inspecting electrical connections.

• Step 1 – Check for prior fault codes: Many Tempstar boards store the last few fault codes. Note any patterns (e.g., repeated 34 or 21) and address those root causes first.
• Step 2 – Inspect electrical supply: Verify tight connections at the furnace disconnect, breaker, and neutral/ground bar. Loose neutrals can cause erratic board behavior.
• Step 3 – Check board environment: Ensure the control board compartment is clean and dry. Look for signs of water intrusion from a leaking condensate line or coil pan.
• Step 4 – Replace control board if persistent: If all underlying issues are corrected and code 45 persists, the Tempstar control board may be internally faulty and should be replaced by a qualified technician.