Furnace frequently locks out and must be manually reset at the power switch to restart.

Safety first: Do not repeatedly reset a furnace without identifying the cause of lockouts.

• 1. Observe lockout pattern: Note whether lockouts occur at ignition, during run, or randomly. This helps narrow down the fault.
• 2. Check and clean basics: Replace the air filter, clean the flame sensor, and inspect pressure switch tubing as described in other entries.
• 3. Inspect wiring harnesses: Look for loose multi-pin connectors on the Thermia control board, gas valve, and motors. Reseat all connectors.
• 4. Record any display codes: If the furnace briefly shows a code before lockout, note it for the technician.
• 5. Professional diagnosis: Persistent lockouts require a technician to monitor operation and test components under load.