I have a Goodman model GMNT 080 4B. The furnace start like normal but when the temperature reaches about 64 degrees I receive an error light. The fan continues to run but the burners do not. I have already tried cleaning the flame sensor but the problem continued.

The error indicator light is flashing 3 blinks. According to the service panel this indicates 'Pressure Switch Failure to Close". Check Venter, Pressure Switch, Vent Blockage.

What does the pressure switch look like? And what does it mean by 'Venter'? I have already check to make sure the vents were open. Thanks in advance.