Most conventional heaters work by turning on to adjust the temperature and then turning back off when your home is warm enough. But, turning on and off every few minutes is called short-cycling, and it’s a sign that there’s a problem with your HVAC system.
There are a lot of possible causes, and they range from inexpensive DIY fixes to major problems. However, in many cases, you can head off an emergency furnace repair — or, worse, needing to suddenly replace the system — if you nip the problem in the bud.
That means that your best bet is to call your HVAC tech right away if you notice short-cycling. But, in the meantime, you can take a few steps to help remedy the situation. With any luck, you’ll fix it yourself.
In this article, we’ll review:
- What Is Short-Cycling In A Furnace?
- Why Does A Heater Short-Cycle?
- Four Reasons A Heater Keeps Turning On And Off
If you notice any of these problems in your Dover, PA home, call or email us at Air Comfort Technologies. We’ll help you fix things fast before the problem gets worse — and becomes more expensive.
What Is Short-Cycling In A Furnace?
Short-cycling is when your furnace turns on and off frequently — more often than it should when things are working normally. The average forced-air furnace should run for 10 to 15 minutes, then turn back off for a while. If it clicks on and off every few minutes, there’s a problem.
Remember, the way it works is that your thermostat recognizes when the temperature dips below the call the setting. Then, it turns on the heater.
Your furnace will push warm air through the vents until your home is actually a few degrees warmer than the setting. That way, it takes longer for the place to cool down below the temperature you want.
As a result, your furnace should run for two or three stretches every hour. If it’s much more frequent, something’s wrong.
Why Does A Heater Short-Cycle?
The two main reasons a heater short-cycles are that something’s not working correctly inside the system. Or, heat is backing up and overheating your furnace.
The first point is pretty straightforward. Today’s HVAC equipment is pretty smart and can sense when something isn’t working the way it should. When that happens, it shuts down as a failsafe to prevent further damage.
But, in most cases, it will try to start back up again when the thermostat tells it to fire up. Then, it trips the failsafe and shuts right back off.
The other reason seems odd: A heater getting too hot? Isn’t that its job?
Well, not quite.
Your heater is designed to distribute heat, not house it. You can damage the inner components of the furnace if it gets too hot inside there. So, when that starts happening, it trips the failsafe shutoff.
Five Reasons A Heater Keeps Turning On And Off
Five specific reasons a heater will keep turning on and off are:
- The Thermostat Is Broken
- Vents Are Blocked
- The Air Filter Is Clogged
- The Heat Exchanger Is Cracked
- The Furnace Is Too Big
We’ve ordered these roughly in order from the easiest to hardest to repair.
The Thermostat Is Broken
A broken thermostat can give bad instructions to your heater. Maybe it’s not reading the temperature correctly. Or, it’s just misfiring. Either way, it can result in short-cycling.
Your first move here is changing the batteries. Then, check the calibration by comparing the room temperature on the display against another thermometer. IF they don’t match, there’s a problem.
Vents Are Blocked
Each vent in your home needs 12 inches of clearance around it. If you have things closer than that to the vent, or if you’ve blocked it completely, then you’re hampering the airflow in your house.
When that happens, heat can back up in the ductwork and dwell in the furnace. Eventually, it results in overheating. You may also notice cold air coming through the vents if the system has to cool itself down.
The Air Filter Is Clogged
You should change your air filter every month. Otherwise, the screen becomes clogged with too much dirt and dust. After all, that’s what it’s supposed to do: prevent that stuff from getting into your HVAC system.
But, a filter that’s way too loaded with debris prevents air from flowing into the furnace. Then, it recognizes something’s wrong and shuts off. Or, it’s getting too hot again and blows cold air to prevent a bigger problem.
The Heat Exchanger Is Cracked
Any number of mechanical problems can cause short-cycling, but we’ll focus on a big one: A cracked heat exchanger. The exchanger is where whatever fossil fuel you’re using — oil, propane, natural gas, etc. — burns to create heat.
When the exchanger cracks, it loses air that should stay built up in that chamber. Then, there’s no combustion, and so the heater recognizes an error. And, previous short-cycling can also cause this problem.
If your system keeps overheating and then blowing cold air, those drastic temperature swings will eventually weaken the exchanger and cause it to break. And, when that happens, you most likely need to replace the furnace.
The Furnace Is Too Big
An oversized furnace won’t work like you think it would. Instead of keeping your house nice and warm, it overheats and shuts back off. There isn’t enough room in the house to accommodate all the powerful forced air.
With nowhere to go, that heat once again backs up into the system, causing it to prevent damage by shutting off. But, your home gets chilly again quickly because it never warmed up the way it needed.
So, the thermostat clicks the furnace back on. But then it shuts back off again, and the (short) cycle repeats.
Unfortunately, there aren’t many easy ways to fix this. You may get lucky and can move your thermostat. The more expensive options are extending your ductwork to account for the extra power or getting a new system altogether.
Emergency Furnace Repair In Dover, PA
We hope you’re able to get to the bottom of why your furnace short-cycles before you’re faced with a system that won’t turn on at all. If you need a pro to help solve the problem in your Dover, PA home, call or email us at Air Comfort Technologies. Or, contact us 24 hours a day, seven days a week for emergency furnace repair if it won’t turn on at all.