York TM9T100C16MP11 Error Code Pressure Switch Stuck Open: Pressure Switch Stuck Open

What Does Code Pressure Switch Stuck Open Mean?

The 3-red-flash code on the York S1-33103010000 board means the draft inducer motor is running but the pressure switch did not close within the expected time. The pressure switch is a safety device that verifies the inducer motor has created enough negative pressure in the heat exchanger to safely vent combustion products. Without this confirmation, the control board will not proceed to ignition.

The inducer motor pulls combustion gases through the heat exchanger and out the vent pipe. If the vent is partially blocked, the motor cannot build enough pressure differential to trip the switch. On York high-efficiency furnaces with PVC sidewall vents, ice formation, nests, and debris in the pipes are the most common obstructions. On standard-efficiency models venting through a chimney, chimney blockages or downdraft conditions can cause the same problem.

A cracked or disconnected pressure switch hose (the small rubber tube connecting the pressure switch to the inducer housing) can also prevent the switch from sensing the pressure change, even when the inducer is working perfectly. This is a visual inspection you can do yourself, though replacing the hose may require a specific size.

How to Fix It: Check the Exhaust Vent and Intake Pipes

What You'll Need

• Flashlight
• Ladder (if needed to access vent termination)
• Gloves

Steps

1. Turn off power AND shut off gas supply Turn the furnace power switch OFF. Turn the gas shutoff valve to OFF (perpendicular to pipe). Wait 5 minutes. If you smell gas at any point, leave the area immediately and call your gas company.
2. Identify your vent system York high-efficiency furnaces (like TM9V 90%+ models) have PVC pipes exiting through a sidewall. Standard-efficiency models (80%) vent through metal pipe to a chimney. Follow the vent pipe from your furnace to find the exterior termination.
3. Clear any vent obstructions Go outside and inspect the vent pipe opening(s). Clear any ice, snow, nests, or debris. If your York furnace has separate exhaust and intake PVC pipes, check both. Shine a flashlight into each pipe to check for obstructions further inside (within a few inches). Do not insert tools deep into the pipes.
4. Visually inspect the pressure switch hose inside Back at the furnace, look for the small rubber hose (about 1/4-inch diameter) connecting the pressure switch to the inducer motor housing. Check that it is not cracked, kinked, disconnected, or filled with water. If it is disconnected, push it back onto the port firmly.
5. Restore and test Turn gas back ON (parallel to pipe). Restore power. Call for heat and listen for the inducer motor to start, followed by a click from the pressure switch, then ignition.

When to Call a Professional

Contact a licensed HVAC technician if:

• The vent pipes are clear and the hose is intact, but 3 red flashes persist
• The inducer motor sounds weak or is not running at all
• There is water pooling in the furnace or around the condensate drain
• The pressure switch hose has water trapped in it
• You hear the inducer running but it sounds strained or different than normal