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“Short Cycling” - No, It’s Not the Latest Fitness Craze

If you’ve noticed that your furnace or boiler seems to turn on and off quite frequently, maybe too frequently, you’re probably wondering if the system needs a repair. While it isn’t uncommon for a properly-sized heating system to cycle on and off multiple times per hour, there comes a point at which the duration of each cycle is too short to efficiently heat up your home.

That’s where we head into “short cycling” territory--and yes, short cycling is a problem.

By the end of this blog post, you’ll know the 3 most important things about short cycling:

  • What short cycling is

  • What causes short cycling in furnaces

  • What causes short cycling in boilers

  • What happens if short cycling is ignored and allowed to continue


Whether it’s a furnace or boiler, if your heating system has suddenly left you out in the cold, you can count on the HVAC specialists at Iceberg Heating & Cooling to complete a repair that’s done right, done fast, and done on time: (734) 375-1119


What is Short Cycling?

“Short cycling” is when a furnace or boiler keeps turning on then off for very short durations. A “short duration” in this instance is generally defined as less than a minute up to a few minutes long. Some short cycling heating systems will turn on and off after just a few seconds.

Troubleshooting Tip: This might seem fairly obvious, but if you suspect that your furnace or boiler might be short cycling, try to time its cycles over the course of half an hour before calling a technician. If your system runs for several minutes at a time, it’s most likely not short cycling.

What Causes Short Cycling in Heating Systems?

There are a number of reasons why a furnace or a boiler might short cycle. The good news is that the solution is not always to buy a whole new system. The solution usually has to do with troubleshooting the system’s built-in safety features.

Common Causes of Short Cycling Furnaces

  • The air filter is too dirty. When your air filter gets to the point where it’s so dirty that it becomes clogged, it inhibits the flow of air to the furnace’s components. This, in turn, can cause the furnace to overheat and shut itself off as a safety mechanism.

  • The thermostat is placed in a poor location. Thermostats are smart--but not that smart. They perceive the temperature to be whatever the temperature is in their immediate surroundings. If you place your thermostat in a location with inconsistent temperature and cold drafts, it can be “fooled” into thinking that the rest of the house is as cold as that one area.

  • The thermostat has gone bad. Just like any other electronics, thermostats can experience technical issues. Your thermostat tells your heating system what it needs to do, so if the thermostat isn’t able to do its job, neither will your heating system.

  • The blower motor is not working properly. The blower motor blows the hot air from the furnace through your house. If it’s not performing this function properly while the furnace is running, the furnace will overheat and shut itself off.

  • Something is blocking the exhaust flue. Because the flue is exposed to the outdoors, like a chimney, sometimes varmints can lodge objects inside of it, activating the flue-limit switch.

  • The ignition system is malfunctioning. As a safety feature, the furnace will usually shut down if the ignition system can’t produce a flame in under four seconds.

  • The furnace is too big. When the furnace is too big for the house, it heats up the house really quickly and shuts off, again and again. Sometimes a furnace that’s improperly sized can even overheat.

Common Causes of Short Cycling Boilers

  • The thermostat is either not functioning or not calibrated properly. If the thermostat’s calibration is off, the boiler will respond in kind.

  • The thermostat is placed in a poor location. If the thermostat is located in an especially cold, drafty, or poorly insulated location, the thermostat will “think” it’s cold all over the house. As a result, it will repeatedly cause the boiler to turn on.

  • The piping by the boiler can’t separate the steam from the water. When this happens, the steam condenses, causing the burner to short cycle.

  • One or more steam traps aren’t working. Steam traps are part of what controls the steam. If they fail in this role, steam can then pressurize the air in parts of the system where that is not supposed to occur. The pressuretrol (which controls when a boiler turns on and off based on steam pressure) will short cycle due to this increasing pressure.

  • The boiler pressure is too high. When this happens, air that’s trapped and compressed by water and steam can cause the boiler to short cycle.

  • The air vents aren’t functioning properly. Normally, the vents prevent the system from trapping and pressurizing air, but when they are not able to, compressed air will alert the pressuretrol to shut off the boiler.

  • The pressuretrol and/or its connection to the boiler are clogged. Sometimes short cycling occurs simply due to a buildup of gunk and sludge in the pressuretrol or the pigtail that links it to the boiler.

  • The boiler is too big. You don’t want your boiler’s ability to produce steam to outdo the system’s ability to condense steam. When the boiler is oversized, this can become a problem.

What Happens If Short Cycling Is Ignored and Allowed to Continue?

A short cycling furnace or boiler may seem like an inconvenience you can live with. While that’s technically true, it’s important to remember these things:

  • Replacing a furnace or boiler that has run its course is quite expensive.

  • Allowing your furnace or boiler to continue short cycling puts a lot of unnecessary wear and tear on it, which can dramatically shorten its lifespan.

  • Therefore, instead of getting 15-20 years out of your furnace or boiler, you could be spending a lot of money a lot sooner than you otherwise would have to purchase a replacement.

  • It’s also worth mentioning the short cycling tends to increase your energy usage, which could be costing you additional money in monthly energy bills.

If you’ve determined that your heating system is short cycling but are uncertain what to do, we can help. At Iceberg Heating & Cooling, we’ll help you discover the root of the problem so that you can get the repair you need while avoiding any needless expenditures. We think our customer Justin K. said it best in a review on December 9, 2018:

“The staff is very helpful and friendly. They won’t recommend any unnecessary work either. I’ve been with them for the last 2 years and I feel that I am in good hands with them.”


Is your heating system short-cycling? Call Iceberg Heating & Cooling today at (734) 375-1119 or contact us online for service in Monroe!


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