One of the most common pressure switch issues is a “stuck” switch that must be manually reset to resume furnace operation.
The switch can become stuck for many reasons. For instance, a pressure switch can become stuck if it’s broken. Likewise, if the circuit is damaged or one of the wires becomes loose, the switch may refuse to come on even if you try to restart the furnace a thousand times.
For this guide, we want to focus on “stuck open” switches. Why would the pressure switch become struck open, and what can you do about it? You can also find other bad furnace pressure switch symptoms.
What Causes Pressure Switch to Stay Stuck Open
The pressure switch can get stuck in an open position for five main reasons. The most common issue is switch-specific issues, including wear and tear and lose connections.
However, issues such as furnace lockout and blocked intake/exhaust paths are pretty common too.
Below we look at how to find the pressure switch, what each issue entails, how to solve it, and the market average cost of fixing the problems.
1. Pressure Switch Problems
Before you look anywhere else, you should begin with the pressure switch itself. The pressure switch comprises many parts that work together to keep your home safe throughout. However, these parts can malfunction from time to time, causing your switch to become stuck.
If it’s stuck in the open position, you should specifically check the hose connecting the switch to the draft inducer housing. Remember that the draft inducer housing “communicates” pressure to the pressure switch via the hose.
Thus, if the hose is damaged (cut, obstructed, or loose at either end), the switch might fail to sense the negative pressure necessary to close the switch. Thus, the switch will remain open.
If it’s merely a blockage, dislodge the debris and test the furnace to see it works. However, if the pressure switch hose is damaged or compromised in another way, it’s best to replace it.
The hoses cost under $5 and are available in most hardware stores. Lastly, if it’s the port on the pressure switch, you may need to replace the switch altogether.
The cost to fix the above issues varies depending on the specific issue. However, generally, you should be prepared with $14 to $44 for DIY and $80 to $200 if you choose to hire an HVAC pro.
2. Furnace Lockout
The furnace can go into “lockout” for many reasons. One of them is a malfunctioned pressure switch. It all starts when you try to ignite the furnace. If the furnace is already experiencing pressure switch issues, it will refuse to come on.
However, being human, you’ll likely try again and again, hoping that the problem resolves. Unfortunately, it rarely works this way. If you try more than twice, the furnace will enter “lockout.”
There are two types of pressure switch-induced lockout – soft and hard. In a soft lockout, you can still try to ignite the furnace. However, it will not ignite.
Instead, only the blower motor will run. Hard lockout is even more restricting. The furnace may refuse to work at all, including the inducer fan.
You need to reset the furnace in most cases, though sometimes you may need to replace the pressure switch. We recommend checking for error codes before you proceed.
Error codes are LED light flashes that signal a problem. If you can see the blinking, refer to your owner’s manual for further guidance.
However, if you can’t see any blinking lights, reset the furnace to see if the problem self-resolves. You can reset the furnace by turning it OFF and then back ON at the main power breaker.
The cost of fixing a furnace lockout varies widely depending on the ideal solution. For example, if turning the unit off and back on at the breaker does the trick, you’ll spend $0. However, if you end up replacing the switch, the total cost might exceed $200.
3. The switch is Temporarily Stuck
It happens, sometimes for no reason at all. Under normal circumstances, the switch opens and closes in response to the pressure from the induction box. However, the switch can get stuck when closed or open, perhaps because something holds a part of it.
The easiest way to know that your pressure switch is temporarily stuck is to check whether the blower fan works when you disconnect the pressure switch. When you first switch on the furnace, the blower fan will not come on.
Additionally, you’ll get a pressure switch code from your furnace. However, when removing a wire from the pressure switch, the blower turns on and runs smoothly.
Often, all you need to fix a temporarily stuck pressure switch is a light tap. However, it’s also a telltale sign of a failing pressure switch. So, you better start making plans for acquiring a new pressure switch from your manufacturer.
It costs between $0 and $200 to fix a temporarily struck furnace pressure switch. Professional replacement is the most expensive.
4. Air intake/Exhaust is Blocked
The gas furnace needs fresh air, abundant in oxygen, for combustion. Similarly, it must effortlessly vent combustion gases produced from the burning process. If either the air intake system or exhaust mechanism fails, the inducer cannot create negative pressure. As a result, the switch will stay open.
So, the stuck switch could signify that the furnace is struggling to provide fresh air for the combustion process or vent the combustion gases. Something could be blocking airflow within the furnace.
You need to find what’s blocking the air intake or ventilation process. Begin with the air intake system. Are the intake vents clean and debris-free? Is something blocking air intake from outside? Perhaps a piece of equipment is sitting directly in front of the furnace? Make sure there’s a 3-foot clearance all around.
Then, check the exhaust system. Is the flue blocked? You can quickly look up your flue with a flashlight to check for debris and dirt. If it’s too sooty, clean it right away. Ultimately, you want to see the light at the end of the tube.
The cost of inspecting your air intake and exhaust system will depend on whether you DIY the entire process or hire a professional. HVAC professionals charge $80 to $150 to inspect and clean the two airflow systems.
5. The Condensate Drain is Blocked
Finally, if your pressure switch is misbehaving, it may also be a sign that your furnace’s condensate drain is blocked. Of course, this only applies to condensing furnaces. However, it’s a pervasive problem because nearly 90% of all furnaces today are condensing units.
Condensing furnaces produce water as a result of lower exhaust pressures. This water is removed from the furnace in various ways. However, the bottom line is that it collects in a drain pan that must be emptied continuously to prevent overfilling.
If the emptying process is compromised, water will back up into the furnace, often spilling over into the pressure switch. When this happens, the pressure switch will instantly call for furnace lockout.
The first step is to empty the drain pan manually. After draining it, reset the furnace, i.e., turn it off and then back on, and see if the pressure switch issue is gone. If so, you now need to troubleshoot the condensate-removal process and fix the underlying issue.
Here too, the cost can be $0 or as much as over $100, depending on the underlying issue and severity of the problem. For instance, if you hire a professional and purchase equipment such as a vacuum, you can easily spend $150+ to drain the condensate.
That’s all you need to know about fixing a pressure switch stuck in an “open” position. Keep in mind that the reasons may not be necessarily the same if the switch is stuck in a closed position. We strongly recommend professional intervention if you run into unchartered territory.