Insights > 3 Reasons Why Your Furnace Turns On and Off Constantly

3 Reasons Why Your Furnace Turns On and Off Constantly


Does your furnace turn on and off frequently? It’s a common problem known as “short cycling.” If not corrected, short cycling can increase your energy bills and lead to costly furnace repairs.

Here’s what may be causing your furnace to short cycle and what you can do about it.

  1. Low airflow. A dirty air filter or blocked or closed registers could be restricting airflow. If your filter becomes clogged, heat can build up on the furnace’s heat exchanger, causing it to overheat and shut off. Change your filter regularly according to manufacturer’s instructions. Also, check all registers to make sure they are open and unblocked by furniture, rugs or other obstructions.

  2. Defective thermostat. Your thermostat controls the heating system, so if your furnace keeps turning on and off, it might be the thermostat. A number of things could cause your thermostat to malfunction. It could need new batteries, or it may have faulty wiring. If the thermostat is located near a heat source, such as direct sunlight or a register, that could be the problem.

    If your thermostat uses batteries, replace them. If you suspect that faulty wiring or the location could be the problem, contact a qualified professional. Also, consider upgrading to a Wi-Fi programmable thermostat. These advanced models optimize savings and convenience and include smart features, such as remote control.

  3. Over-sized furnace. A furnace that's too big for the space will likely short cycle. Why? The larger unit will heat the house too quickly then abruptly shut off. Once the temperature drops, the cycle is quickly repeated. One possible solution is to reduce the cycles per hour heat setting on an advanced thermostat (say, from five to three). The trade-off is wider temperature swings. Otherwise, you'd have to replace your furnace with a new unit that's properly sized for your home.

    Contact a trusted, qualified installer and make sure your new furnace or heat pump is ENERGY STAR® certified. ENERGY STAR heating systems use less energy than standard units while providing the same level of comfort.

That's not all

There could be other issues causing your furnace to cycle on and off frequently. It could be defective fan limit switch, a corroded flame sensor or a poorly designed duct system. Problems such as these require the attention of a qualified HVAC professional.

To help prevent costly maintenance issues and ensure optimal performance, have your heating system cleaned and inspected at least once a year.

Entergy offers energy efficiency programs that can help you save energy and money in your home. Check out what's available in your area.

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