3 Unexpected Causes Of Furnace Pressure Switch Errors

Modern HVAC systems typically include a control board that will flash warning lights or numerical error codes whenever they experience a problem. These codes are most valuable to technicians, but they can still help you as a homeowner understand why your furnace isn't working. You can usually check these codes by referencing a table you should be able to find in your furnace's manual.

One common code you may find will relate to the pressure switch. The furnace won't operate without adequate negative pressure to pull exhaust fumes from the combustion chamber. The pressure switch proves this condition exists, and you'll see an error code if there's insufficient pressure. A failed draft inducer is one potential cause, but one of these three unexpected failures may also be to blame.

1. Clogged Intake or Exhaust Flow

Your furnace will need at least one piece of plumbing to allow exhaust gases to escape your home. Modern condensing units typically use PVC piping, while older or standard efficiency models may still use a metal flue. Whichever type of exhaust plumbing your furnace uses, an obstruction will prevent the draft inducer from creating an appropriate amount of pressure.

You can easily check for obstructions by looking where the exhaust pipe exits your home, although you should ensure your furnace is off before attempting this step. If your furnace uses a separate intake pipe, it may also have a blockage. Note that obstructions can occur deeper in the pipe, and if you can't easily see one, you'll probably need a professional to help.

2. Clogged Condensate Drains

Surprisingly, a clogged or improperly installed condensate drain can be another potential issue. The condensate drain is necessary to remove moisture that condenses from the cooled exhaust gases, and a clogged drain will allow water to backfill into your furnace's heat exchanger. When this situation occurs, it will potentially block the passageways the pressure switch uses to detect drafts.

Cleaning your condensate drain should be a normal maintenance routine. However, neglected drains can become clogged, and improperly installed drains may clog frequently. If your condensate drain needs cleaning too often, an HVAC technician should confirm that it's installed correctly and meets all local building codes.

3. Faulty Pressure Switch

Of course, a faulty pressure switch may also cause your furnace to throw this error code. Pressure switches will typically fail in a way that causes your furnace to stop running, ensuring that a bad pressure switch doesn't create a dangerous operating condition. Because your pressure switch is a safety feature, it's important never to attempt to bypass its operation.

Likewise, you shouldn't condemn your pressure switch because you can't see any other problems. A technician must test the switch for proper operation before confirming it's to blame. This diagnostic step is critical to avoid needlessly replacing a good part and failing to solve your underlying problem. 

For more information about furnace repair, contact a local company.