pressure switch for a furnace

A pressure switch in a furnace serves as a kind of safety device, detecting for negative pressure, incorrect venting air pressure and proper combustion airflow. If improper conditions are detected, the pressure switch will shut down the furnace ignition to prevent unsafe operation. More often than not, a problem with a pressure switch, such as the switch staying open, is an indication of a problem elsewhere in the furnace that needs to be addressed.

Open Switch

When the vent system in a furnace is working properly, the induced draft blower will close the pressure switch. But when a pressure switch won’t close and no heat is being produced, common problems include:

  • Debris buildup  in draft blower housing
  • Failed motor
  • Cracked heat exchanger
  • Blocked condensate drain
  • Stuck pressure switch
  • Plugged vent pipe

Pressure switch problems can differ between mid-efficiency and high-efficiency furnaces.

Improper Piping Size and Installation

In many cases, a pressure switch problem relates back to the installation or length of combustion air and flue piping or condensate piping within the furnace system. If the length of flue piping is too great or the pipe diameter too short, the pressure switch may open.

Another common cause of an open pressure switch is the buildup of condensate inside the furnace from improper condensate piping installation. Your Gillece HVAC Technician can inspect your heating system to see if any piping has been installed incorrectly or is improperly sized.

Defective Switch

Sometimes the pressure switch itself is defective and can be replaced. A professional HVAC Technician will use a specialized gauge or manometer in order to find out if the switch is in fact defective and causing the problem in your furnace.

Troubleshooting by Professional Technicians

Troubleshooting a furnace pressure switch can be tricky. With a complex system and commonly misdiagnosed problems, it’s important to consult a professional HVAC Technician if your furnace stops working or the pressure switch won’t close. Gillece Heating Experts are experienced, continually trained and on top of industry-leading technology to help troubleshoot and diagnose furnace and other heating system issues.