Has your gas furnace stopped working? Or has the efficiency slowed down to the point that a system shutdown seems inevitable? There are several potential causes for a malfunctioning gas furnace, but the pressure switch is always a good place to check.

The pressure switch is a safety feature that works a little differently than something like a limit switch. When the pressure switch closes, electrical current is allowed through to start the igniter and the heating process. When the switch opens, the current stops so that the system doesn't overheat.

You can check to make sure the pressure switch is working by using an ohmmeter and the instructions in your owner's manual. If the reading shows that the pressure switch has failed, you will need to replace the part.

Only perform this job if you feel confident working around electricity. Call a furnace repair company, such as Absolute Comfort Heating & Air Conditioning, if you aren't comfortable.

Things You Need:

• Screwdriver
• Owner's manual
• Socket wrench
• New pressure switch

Step 1: Access and Unhook the Old Pressure Switch

Turn off power to the furnace on the breaker or fuse. Remove the upper access panel by twisting its fasteners or removing its screws. Set the panel aside.

Locate the pressure switch using your owner's manual for help, if needed. Generally, it will be in the upper left corner of the area revealed when you removed the access panel.

Disconnect the wires attached to the pressure switch. The wires should pull out easily and are just as easy to reconnect in the right positions so you don't need to fret over mixing the wires up.

Remove the pressure tube from the bottom of the pressure switch. The tube connection can be firm so use a screwdriver to pry the tube free but still be careful so you don't puncture anything.

Use a socket wrench to undo the fastener holding the pressure switch in place. Remove the pressure switch, which will also remove the bracket it was attached to. Set the old switch aside on the table until the next step.

Step 2: Install the New Pressure Switch

Compare the pressure ratings written on the back of the old switch with those on the new switch. You want to make sure the part you're putting in is the same pressure or you risk shutting down your system.

Fasten the new pressure switch into place using the fastener put through its attached bracket and secured with the socket wrench. Hook the wires back up and then the pressure tube.

Return the access panel doors and fasten it in place. Turn the power back on for your furnace and run a cycle to ensure that the new switch fixes your problem. If the problem persists, call in a furnace repair technician for help.