A furnace relies on negative pressure to vent its exhaust safely outside. The furnace pressure switch is the part of the furnace that ensures there is that pressure so that the furnace can operate. If your furnace pressure switch is malfunctioning, you might notice all kinds of problems with the furnace. In fact, it may not turn on at all.
Let’s walk through how a furnace pressure switch works and what you can do if there is a problem with yours.
How Does a Furnace Pressure Switch Work?
A pressure switch determines the pressure in the furnace. It starts out open and reassesses the pressure when the furnace turns on. If the furnace turns on properly and creates negative pressure, which allows the exhaust to leave the furnace safely. When the pressure switch notes this negative pressure, it closes.
It is attached to the electrical circuit so that when it closes, the furnace can fire up. This ensures that if the furnace doesn’t have negative pressure, and therefore isn’t venting properly, that the furnace can’t turn on. While you might find that this is frustrating if your furnace isn’t working, it is an important safety feature that prevents exhaust fumes from getting into your home.
In fact, if the pressure changes in the furnace for some other reason, then the furnace pressure switch will close and stop the furnace from running in unsafe conditions.
Problems with Furnace Pressure Switches
Many different problems can develop with your furnace pressure switch that will stop your furnace from working. Here are a few possibilities and their fixes:
- Loose hoses: The pressure switch has two hoses, one on each side. Both should be attached, and if they come loose, they can prevent the pressure switch from closing, which prevents the furnace from turning on. Your HVAC professional can reattach them.
- Debris on switch: Debris in and on the switch can interfere with the proper function and eventually lead to rust and corrosion. Your switch should be cleaned yearly as part of your furnace maintenance.
- Crack or hole in tube: If either tube or hose has a hole or crack, then it will relieve the pressure in the pressure switch, so it won’t operate properly. You’ll need your HVAC professional to replace the tube, and probably the other as well, as they usually develop holes out of old age.
- Broken switch: The furnace switch can be broken by another malfunctioning part in your furnace. For example, a blockage in the inducer fan can break a switch entirely, so it will need to be replaced.
Don’t Ignore Long Term Problems
It’s worth mentioning that long-term problems with the furnace pressure switch can cause some furnaces to go into lockout mode, where it won’t work even if you fix the pressure switch. You’ll need to completely replace the switch and reset the furnace so that it will turn back on. Your HVAC professional can handle this lockout for you. And if you need help with your furnace in Tracy, or anywhere in the greater Tracy area, we’ll be happy to assist.