Furnace Pressure Switch Stuck Open

Furnace Pressure Switch Stuck Open – How to Troubleshoot

If there’s one thing that modern technology has taught us, it eases our lives tremendously. However, the more complicated the modern devices easing out our lives are, the more challenging repair and fixes will be.

It’s the case of furnaces that come with a long list of best performance features and incredible accuracy. However, furnaces have an intense operation process, so they have to take a lot of wear. With furnaces running and stopping all the time, it’s perfectly understandable why they’re never trouble-free. The risk for a furnace to develop issues at some point is rarely null.

What’s the furnace pressure switch?

The pressure switch is supposed to control the pressure within your furnace. It’s supposed to stay in an open position. After your furnace has started, the draft inducer motor starts running, generating negative pressure to eliminate the combustion gases.

Once the pressure switch identifies the pressure, it will switch to the closed position, ending the electrical circuit and making the furnace go through the next phases. The furnace will fire up the burner and blower for generating and spreading heat. When the drop in the pressure doesn’t happen anymore, the furnace isn’t properly vented, making the switch not to close. The furnace won’t fire anymore; if it does fire, it will stop right away.

Keep in mind that furnaces use lethal carbon dioxide, so when the furnace isn’t venting properly, the harmful gases will get back into the house.

Should you plan to address the pressure switch problem on your own, always stay safe and begin with turning off the power to the furnace from the switch located on or close to the furnace. It looks like a regular light switch. Should you be unable to find it, it’s best to turn off the furnace breaker in the breaker box. It’s recommended that you lock the electrical box in several areas while addressing any electrical device to make sure that nobody will turn the power on by accident.

What makes the pressure switch become stuck open?

It’s not always the pressure switch that makes it remain open, and several problems with the furnace could stick it too. Here are the possible causes and fixes as well.

Take a look at the pressure switch.

You will need to remove the primary access panel and observe the hoses attached to the furnace pressure switch. They’re supposed to be in good condition, without any obstruction, and attached at both ends.

The fix

If the hoses aren’t connected anymore, you have to reconnect them. Make sure also to remove debris and replace the cracked/damaged hoses. You will need to replace the pressure switch if the hose ports (where the hoses are connected to the controller) present any cracks.

You should utilize an ohmmeter to know if the pressure switch is opening/closing correctly when the request for heat is sent. Make sure that the furnace’s power is turned off. Take off one of the power hoses, blowing on it. Utilize the ohmmeter to verify if the pressure switch is working correctly. Continue with sucking on the power hose, checking the button with the ohmmeter.

You will have to take a look at the secondary exchanger and the inducer to observe if the exhaust ports are blocked in any way.

A problem if the in the furnace could cause the pressure switch stuck open. The plunger may not pull entirely and may bob around as the pressure increases inside the furnace. Use a wire brush and cloth to remove dirt and blockages from the inducer and secondary exchanger. Cleaning of the drain tubing could also be necessary; blow out on it while blowing into the secondary exchanger for maintaining the pressure.

It will cost you anything from $ 15 to $45 to replace the pressure switch, but it’s typically around $25. If you’re going to call the professionals, the minimal service fee is $75-$80, to which you will add the costs for the replaced parts.

Furnace lockout

As the thermostat sends the heat request, the IFC (integrated control unit) will control the pressure switch. At this moment, the button should be open and stay so until it identifies negative pressure. When the pressure switch is in a closed position before negative pressure generated by the inducer motor, the IFC will block the furnace ignition phase. When the IFC identifies repeated break or prolonged break in the ignition phase, it will place the furnace into lockout mode.

The fix

You will have to replace the pressure switch or reset the furnace. Resetting the furnace isn’t complicated. You only need to turn off the primary power breaker, placed in the house’s electronic breaker box.

Many modern furnaces come with panels and flash a code; a light will blink in a specific sequence. You need to check the manual to see what the code means and what you should do to fix the problem.

The pressure switch is temporarily stuck.

When the blower fan doesn’t turn on, and you identify a pressure switch error code, you will have to remove the wire from the pressure. Should the blower fan turn on again, the pressure switch was stuck closed.

The fix

Gently tap for opening the stuck-closed pressure switch, which makes the blower to start. It means that the lousy pressure switch remained stuck closed, and you have to replace it with a new pressure switch. The pro pressure switch replacement ranges from $14 to $200.

What other problems could the pressure switch present?

You can always test a stuck-open pressure switch by recycling the furnace. You will have to remove the wire connections from the pressure switch.

As the thermostat sends the heat request, the draft fan will begin to run. As the fan is running, you may short the pressure switch wires (use a jumper for manual connection). If your furnace starts, the problem is with the pressure and with the pressure switch.

Blocked air intake or exhaust

Every furnace requires fresh air for proper combustion. After combustion takes place, the combustion gases have to be vented. When the intake or the exhaust is blocked, the inducer fan won’t generate negative pressure, causing the pressure switch to stuck open. However, the pressure switch isn’t stuck, but it’s doing its job.

Bird nests, wasp nests, snow, ice, or leaves may block the vent or the intake.

The fix

Take a thorough look at the flue. When your furnace has an 80% AFUE rating, the vent is probably on the roof. For the high-efficiency condensing furnaces, the vent is probably located on an outside wall of the house.

Either way, you have to ensure that the air intake is clear and clean. Also, examine the air vents on the furnace cabinet, cleaning if necessary.

As long as you’re doing it safely, it should cost you nothing to clean the vents. If you’re calling the professionals, expect to pay anything from $80 to $180 for removing the debris.

Blocked condensate drain

High-efficiency furnaces (AFUE rating over 90%) come with a condensate drain, which may become blocked. Condensation backup will go back into the blower fan’s housing, generating problems such as pressure switch stuck open.

The fix?

You may try solving the problem of a blocked drain line; proper equipment and products will be needed. You will also have to adjust the condensation trap so that the water gets to the drain and the furnaces gases get collected.

You will spend anything from zero to $100 for the equipment for cleaning, like a shop vacuum.

However, if you’re calling the HVAC technician, it will cost you anything from $80 to almost $300. If your furnace is rather old and repair costs are higher than anticipated, it may be a better decision to buy another furnace.


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