December 15, 2022
Technician Fixing Furnace Pressure Switch Foothill Ranch, CA

Turning on the heat in your Foothills Ranch, CA home is as easy as adjusting your thermostat. With just a slight change to your preferred temperature, your heater roars to life, and your living space is filled with warm air. However, despite how simple things are on your end, it’s actually a very complex process behind the scenes. This is especially true with gas-fired furnaces that both burn fuel and ensure that building residents aren’t exposed to the harmful byproducts of combustion. Your furnace pressure switch plays a vital role in this process. If it stops working, your supply of warm air will stop too.

What Does a Furnace Pressure Switch Do?

Furnace pressure switches are built-in safety features that limit the risk of carbon monoxide (CO) exposure and prevent furnace fires and explosions. They do so by automatically shutting combustion down when negative motor pressure is detected. In some instances, this could mean having the furnace stop altogether. In others, pressure switch shutdowns simply stop moving air from being heated.

Malfunctioning pressure switches may incorrectly detect negative air pressure due to their own structural issues. For instance, if their diaphragm flaps are ruptured or get stuck, airflow is impeded, and pressure readings will suffer.

Furnace Pressure Switches and Back Drafting

Negative motor pressure is a strong indication of back drafting. When your furnace combusts fuel to produce heat, it does so incompletely. This creates carbon monoxide and other harmful contaminants that must be routed out of your home. If everything is working normally, these contaminants flow out of your system, through your furnace vent, and into the outdoor air. In the case of negative motor pressure, these gases are sucked back inside.

Why Did Your Furnace Pressure Switch Cut Off?

If you have lukewarm air coming into your home, back drafting could be the cause. However, this could also mean that your pressure switch has been damaged or that it has reached the end of its life span. Like all other components in your heating system, furnace pressure switches eventually get worn out. Given that they are key safety features, furnaces are designed to stop functioning until they’ve been replaced.

Pressure switches can also shut your furnace off if they fail to close properly. Several common causes of pressure switch malfunction include:

  • Ruptured diaphragms
  • Flue obstructions
  • Damaged pressure switch hoses
  • Water in pressure switch houses

Only a licensed HVAC technician can accurately determine why your furnace is no longer performing as it should. Our team can find out why your pressure switch has caused operational problems, if it’s done so at all. Although you might notice the signs of a damaged or malfunctioning pressure switch, it’s unsafe to assume that the failure of this component is at fault. Until you can be sure that your furnace venting system isn’t back drafting, it is unsafe to turn your furnace on.

Troubleshooting and Resolving Pressure Switch Issues

When we address pressure switch problems, we start by ruling out all possible sources of exhaust leaks. After all, the shut-off function of a pressure switch is designed to protect you and everyone else in your household. We’ll check for obstructions at the flue pipe, and we’ll make sure that your home doesn’t have negative air pressure.

After back drafting and other combusting-related problems have been ruled out, we’ll check the integrity of the pressure switch and its hose. We’ll also make sure that this hose isn’t filled with water or blocked by a solid obstruction. Next, we’ll verify that the collection chamber’s port that leads to the pressure switch isn’t clogged. If it is, we’ll remove this debris and then test the pressure switch to see if proper functioning has been restored.

If the diaphragm on your pressure switch is stuck or ruptured, the pressure switch must be replaced. Although gently tapping a stuck diaphragm will produce a short-term improvement, it won’t be long before this component fails entirely. Problems at the pressure switch diaphragm often create a soft, flapping sound when the heater is on, and they’re a sure sign that the pressure switch is too old to continue doing its job.

Negative Air Pressure and Your Pressure Switch

When pressure switch problems are the result of negative motor pressure, you may have a serious issue on your hands. Rather than removing and replacing a single component (the pressure switch), it may be necessary to assess and completely revise your home’s envelope. Your home’s envelope is defined by the overall airtightness of the building. Every time you add new insulation or seal up air leaks, you tighten your home’s envelope. This reduces the amount of energy that your furnace and air conditioner must consume to create the indoor temperatures you want.

Having a tight home envelope is generally viewed as a good thing. Insulating measures limit spending, reduce energy waste, and make it possible for people to maintain modest carbon footprints. However, there is such a thing as having too much airtightness. When a home that uses furnace vents and other venting systems is completely airtight, air constantly leaves the building, but it never gets replaced. Over time, the result is negative air pressure.

Negative air pressure isn’t a static condition. Instead, it’s one that seeks to correct itself. Air will be drawn into your home from any possible avenue. One of the most viable points of ingress is your furnace vent. Instead of having exhaust gases be pushed out and away from your living environment, outdoor air will flow in, and exhaust gases will come with it. This is known as back drafting. When it’s detected via negative motor pressure, the pressure switch will halt fuel combustion right away.

Different Types of Pressure Switches

Just as there are different types of heating systems, there are also different types of pressure switches. Moreover, single-stage, gas-fired furnaces have just one pressure switch while two-stage furnaces have two.

There are electronic pressure switches and electromechanical or mechanical pressure switches. Electronic pressure switches use electric sensors to detect anomalies in combustion and venting processes. Mechanical pressure switches detect anomalies via diaphragms, Bourbon tubes, pistons, and other mechanical means. Although electronic switches are the most resistant to shock and vibrations, mechanical pressure switches are more reliable.

Pressure Switches Have a Limited Life Span

If correctly sized, properly installed, and well-maintained, the average furnace will last about 15 to 20 years. Comparatively, the maximum life span of a furnace pressure switch is about 10 years. Thus, if you’ve had your furnace for a decade or more and have not had problems with its pressure switch in the past, these issues are probably looming just around the corner.

During our furnace tune-up service, we carefully assess the age and condition of all furnace components. Our technicians know how long each component is designed to last. This allows us to change-out things like aging pressure switches before they outright fail. Not only does this ensure reliable heater operation, but it also provides a higher level of furnace safety.

Since 2003, White Mechanical, Inc. has been proudly serving residents of Foothills Ranch, CA and the surrounding area. We offer commercial and residential air conditioner and heater installation, maintenance, and repair services. We also offer preventative maintenance plans. If it’s time to have your furnace pressure switch replaced, give White Mechanical, Inc. a call!

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