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Problems With High-Efficiency Gas Furnaces: Are The Pressure Switches Faulty?

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High-efficiency gas furnaces combine excellent heating performance with very low running costs, but they are not perfect. They can suffer from mechanical malfunctions just like any other type of furnace.

If your high-efficiency furnace is not functioning properly or refuses to function at all, one or more of its pressure switches may be faulty. These small but vital components are used in all gas furnaces but serve a particularly important role in high-efficiency models. Any problems with your furnace's pressure switches must be repaired as soon as possible.

What Are Pressure Switches In High-Efficiency Gas Furnaces?

 All gas furnaces contain pressure switches, which monitor the pressurization of the exhaust gases inside the furnace. They are designed to prevent back-drafting, a serious problem that can put your life at risk.

When gas furnaces burn natural gas or propane, they create toxic exhaust gases, which are expelled through the furnace's flue by a draft inducer fan. If this fan fails, or the flue starts to leak, exhaust gases can re-enter the furnace, and may start to leak out of the furnace housing and into your home. These leaking exhaust gases are potentially deadly if inhaled.

When exhaust gases re-enter a furnace, the pressure of the gases inside the furnace rises. If pressure levels become too high, the furnace's pressure switch automatically shuts down the furnace, preventing dangerous leaks.

High-efficiency furnaces boost their performance and efficiency by recirculating exhaust gases while they are still hot, extracting as much heat as possible. This makes back-drafting and leaks even more dangerous, so high-efficiency furnaces must have functioning pressure switches at all times. Most high-efficiency furnaces have two or three switches.

What Problems Are Caused By Faulty Pressure Switches?

If one or more of the pressure switches in your high-efficiency furnace fails, the furnace's electrical circuit is automatically broken, and the furnace will not function. Most high-efficiency furnaces have dedicated warning lights that flash if a pressure switch has failed or will show a fault code on their digital readouts. 

If a pressure switch malfunctions but does not fail, your furnace may start short-cycling. This occurs when a faulty pressure switch shuts off the furnace's power supply too soon before exhaust gas pressures reach dangerous levels.

During short cycling, your furnace will deactivate a few minutes after activation. After a little while, the thermostat will reactivate the furnace, only for it to deactivate itself again a few more minutes later. A short-cycling furnace uses a lot of energy and produces very little useful heat.

What Should You Do If Your High-Efficiency Furnace Has Pressure Switch Problems?

If your high-efficiency furnace fails to activate or starts short-cycling, you should call in a professional furnace repair service. These services will inspect your pressure switches for signs of damage, and will also inspect other components in your furnace that may be causing your problems. 

In most cases, furnaces pressure switches cannot be effectively repaired without causing irreparable damage to their housings. If your high-efficiency furnace has faulty switches, they will almost certainly need to be replaced. Fortunately, replacement pressure switches are relatively inexpensive and can be fitted quickly by professional service personnel, so your furnace should be back up and running the same day.