How to Troubleshoot Furnace Pressure Problems
If you are having pressure problems with your furnace, this article can help, but it's important to follow these safety guidelines before trying to diagnose the problem: Always read the safety instructions and warranty information that came with your heater. Be sure to turn off the electrical power and/or gas. And be sure to read this entire list of instructions before starting the troubleshooting process. Does this Spark an idea?
Instructions
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Verify that the opening where the draft inducer (it may be metal or plastic, depending on your furnace) attaches to the pressure switch tube is actually open. It may attach at the top, bottom or center of the draft inducer.
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Check to see that all safety devices are closed. This includes all limit controls. These items are programmed to prohibit the ignition process from starting as a safety mechanism, so if they are not all closed, your furnace will not start.
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Test the pressure switch itself to see if the problem lies in the switch. Using a volt ohm meter, place one meter probe on a lead wire going to the pressure switch and "ground" the other probe. To "ground" is to attach the probe to metal that is part of the furnace. The meter, which you should have set to Volts AC, should register 24 or more volts. If it does not, the pressure switch is the problem.
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Test the rollout limit switch using the ohm meter. Place one meter probe on one terminal of the rollout switch and "ground" the other probe. Test both the top and bottom terminals of the rollout switch. If the meter reads 24 volts or more for both terminals, the rollout limit switch is OK. However, if you do not get the desired voltage reading, the problem could be a stopped-up vent, bad pressure switch or bad drain line, requiring expert help.
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Tips & Warnings
Keep your user manual on hand during the troubleshooting process to help you identify different parts of the furnace. If you have never used an ohm meter before, you should also read these instructions in their entirety.
If you smell gas while you are testing your furnace or any other appliance, call emergency personnel and leave the house immediately.
