Display shows 'BDS' and heater will not start; blower may not run on fan‑assisted models.

Safety first: Turn off power and gas. Fan and pressure switch circuits are safety‑critical.

Steps to address BDS error:

• Check blower operation: On call for heat, listen for the blower. If it does not start, inspect the blower motor wiring and capacitor (if used). Replace the blower assembly if seized or burned out.
• Inspect intake and exhaust: Ensure the combustion air intake and exhaust vent are free of obstructions (leaves, nests, snow, etc.). Clear any blockages.
• Inspect pressure switch tubing: Verify the silicone tubing from the blower housing to the air pressure switch is intact, not kinked, and firmly connected.
• Test pressure switch: With power OFF, disconnect wires and check continuity while manually applying slight suction to the tubing. The switch should close. Replace if it does not respond.
• Check wiring to control board: Confirm the pressure switch leads are correctly connected to the control board terminals and not corroded.

Note: If the blower runs but BDS persists, the pressure switch or its sensing port may be blocked and require cleaning or replacement.