Furnace short-cycling. A term you probably haven’t heard until it became a problem.
Short-cycling means that your furnace is turning on and off repeatedly, which means it’s not running a full cycle.
But you’re probably wondering:
“Why is my furnace short-cycling and how can I get it to stop?”
Both are great questions and we are going to answer them in this post.
What Does Short-Cycling Look Like Anyway?
Before we can tell you how to stop the madness, you need to understand the problem. A furnace that is in good working condition and is the appropriate size for your home will experience 3 to 8 power cycles per hour.
Yes, that means that your furnace could turn on and off up to 8 times in an hour and be totally normal.
However, if the furnace turns on and off more than 8 times an hour, it doesn’t automatically mean you have a furnace that is short-cycling. Frustrating, right?
Here’s the key difference:
The run time.
A short-cycling furnace will likely only run for a minute or 2, possibly even less, before it turns off. Whereas a normal furnace will run several minutes each time it comes on.
Now that we’ve cleared that up, let’s look at how you can (hopefully) put a stop to the short-cycling.
1. Check (and Change) the Air Filter
We know it’s annoying to hear so much about air filters and replacing them often. They can’t really be that important, can they? Yes, they are, and it’s not only because you deserve to breathe clean air. The filters are designed to keep all the inner-workings of the HVAC system clean.
Your furnace has a High-Limit Switch which is a safety feature designed to turn the furnace off if it gets too hot.
Now, imagine what happens when your furnace turns on and tries to send a constant flow of air to the heat exchangers but can’t because there’s a wall of dust and dirt (a clogged filter) in the way. Air flow is blocked, the heat exchangers continue to heat up and get too hot, and the furnace shuts off. Over and over again.
The simple solution: Turn your furnace off and check the filter. If it’s dirty or it’s been 3 months or more since you changed it, put a new, high-quality filter in place. Turn the furnace on again.
If it’s still short-cycling, move on to the next option:
2. Check the Thermostat
There are a couple of different options for troubleshooting your thermostat. Let’s start with the easiest.
A thermostat that has low batteries could cause the system to shut off and turn on again. To see if this is the problem, put fresh batteries in your thermostat and let the system run for about an hour to see if the problem is solved.
If fresh batteries don’t fix it, it could still be the thermostat. Grab a screwdriver and open it up. Before you panic at the sight of wires, keep in mind that these are low-voltage wires and they won’t hurt you. Grab a pair of rubber gloves and proceed with caution. Remember – never touch the brown and red wires together or you will blow a fuse inside the furnace.
Unscrew (or unclip) the red and white wires to gain access to them. Carefully touch the two wires together and keep together for about 5 minutes. The wires need to be firmly together the whole time, or this test is useless.
If the furnace runs the whole time you’re holding the wires together, you’ve got a bad thermostat. If the furnace still short-cycles, the thermostat is not the cause. Either way, keep reading.
3. Call an HVAC Professional
If you’ve reached this point, there isn’t much else you can do on your own. If you discovered in step 2 that the thermostat is bad, you can buy a new one and replace it yourself if you’re comfortable with that. If not, call a professional to come out and replace it for you.
If it’s not the air filter, thermostat batteries, or thermostat, you’re at the end of the DIY line. Call a professional and let them know the things you checked. They will come to your home and determine what’s causing the short-cycling and let you know what they can do to repair your furnace.
Furnaces can be frustrating, confusing things, but you still need one working well in your home. If you’re experiencing problems with your furnace, don’t hesitate to give us a call to schedule service.