Boiler displays PS or Pressure Switch Open; fan may run but burner does not light.

Safety first: Turn off power before removing covers. Do not operate the boiler with venting disconnected. Combustion gases are hazardous.

• Inspect venting: From the boiler to the termination, check the PVC or polypropylene intake and exhaust pipes used on Laars condensing boilers. Look for snow, leaves, bird nests, or debris blocking the terminations. Clear any obstructions.
• Check condensate drain: Locate the condensate trap and drain tubing. If the trap is full of sludge or the tubing is kinked or frozen, water can back up and affect the pressure switch. Clean the trap and ensure the drain line slopes properly and is not blocked.
• Inspect pressure tubing: Find the silicone or vinyl tubes running from the blower housing to the air pressure switch. Ensure they are firmly connected, not cracked, and free of water. Gently blow through the tubing (with power off and tubing disconnected) to confirm it is clear.
• Test operation: Restore power and call for heat. Listen for the inducer fan. If the fan runs but PS remains, the pressure switch may be faulty or the fan not producing enough pressure.

When to call a professional: If the pressure switch continues to show open after vent and condensate checks, a technician should test the switch, inducer performance, and combustion air system.