Here’s a scenario that will sound all too familiar to many homeowners here in the Princeton area: Your home feels slightly chilly, so you adjust your thermostat to get the heating system running. Your furnace turns on and operates just fine, only to shut off after a few minutes. Soon after, it turns back on and begins to warm your home once again, only to shut off once more.
This frequent on-and-off of your furnace is called short cycling, and it may happen for a variety of reasons. Usually, the problem can be traced back to an overheating heat exchanger, a dirty flame sensor rod, or an oversized furnace.
Overheating Heat Exchanger
A heat exchanger is the part of a furnace that heats the air. If there is low airflow in your furnace, the heat exchanger will get too hot. This, in turn, will trip the high limit switch, which shuts off the furnace to protect it from damage.
That low airflow in your furnace can have a few different causes. The air filter in your furnace may be dirty, causing the blower to struggle to pull air in over the heat exchanger. In this case, you would need to clean or replace your furnace’s air filter. Your furnace may have a dirty blower wheel, causing it to slow down and deliver less air over the heat exchanger. In this case, you should hire a technician to clean the blower. You also might have too many air supply vents closed, slowing down the blower and reducing air flow. Whatever the cause of low airflow, if it makes your heat exchanger overheat, you’re not going to have a well-functioning furnace.
Dirty Flame Sensor Rod
Does your furnace turn on a few times for four to seven seconds at a time, and then shut off for a while? This could be due to a dirty flame sensor rod. The flame sensor rod is a safety device in your furnace that shuts the gas valve when it does not detect a flame in the burners. If that rod has collected soot and become dirty over time, it may not detect a flame in the burner right away. When this is the case, it will signal the gas valve to shut, cutting off the supply of gas to the burner and putting out the flame. Cleaning or replacing the flame sensor rod will typically get your furnace running normally once again.
If you recently replaced your furnace, or if short cycling has been a problem with your furnace for years, it could be due to an oversized furnace. An oversized furnace will heat your home too quickly, causing it to turn off and on often to keep your home comfortable. If you recently replaced your furnace, you should definitely contact the installer to have them address the issue. If you have an older furnace, now may be a good time to consider investing in a new, energy efficient, and properly sized furnace.
As you can see, it isn’t always easy to determine why a furnace keeps shutting off. The professionals at Princeton Air have the skills and expertise necessary to accurately diagnose what’s going on with your furnace. We can also maintain your furnace to make sure none of these issues arise, and if short cycling is undermining your home’s comfort, we’ll help you solve the problem!