What to Do if Your Furnace Keeps Turning On and Off

What to Do if Your Furnace Keeps Turning On and Off

Furnaces are calibrated to turn on and off based strictly on changes in indoor air temperature. But sometimes, furnaces will begin turning on and off too rapidly to be responding to temperature variations.

This is not normal behavior and the problem is unlikely to clear up on its own. This pattern of functioning is called short cycling, and it is a sign of trouble that you cannot afford to ignore.

Short Cycling Means Trouble

Furnaces normally shut on and off between three and eight times per hour, and in colder weather a quick pace in cycling should be expected. But when your furnace is short cycling it will switch on and off every two or three minutes, which indicates a malfunction or glitch somewhere in the system.

Three Common Causes of Short Cycling

Your furnace’s short cycling could be a sign of many things, including:

#1 Dirty air filter

When air filters aren’t changed regularly, they can become clogged and dirty. This leads to restricted air flow through the intake vents, which could cause the heat exchanger to shut down soon after the furnace is turnn’t cool properly and would be in danger of burning out if it kept running.

Experts estimate that up to 90 percent of short cycling is caused by a died on, since it worty air filter, which is a testament to how lax people are about changing their air filters on time.

#2 Thermostat problems

Reliable thermostat performance is required for a furnace to work properly. But if your thermostat isn’t working it can cause a range of system operating troubles, including short cycling.

#3 An incorrectly-sized furnace

If your furnace is too big for your home, it will tend to heat up the rooms in your house too quickly, possible leading to a pattern of short cycling. This may seem like a sign of superior efficiency, but a furnace that short cycles for this reason will wear out much more rapidly than it should.

What Can Be Done?

When your furnace is short cycling, you can do some troubleshooting on your own before you summon a professional. Here are the steps you can take that may solve the problem:

#1 Check your air filter

Air filters that have been in place for an extended period of time should be replaced, and a good rule of thumb is to get a new filter at the beginning of each heating and cooling season. If you’ve been using a cheap fiberglass model, try upgrading to a good-quality pleated filter with a MERV rating of 9-12.

Once the filter has been replaced, the chances are good the short cycling will stop. If it doesn’t, you can move on to the next possibility.

#2 Check the thermostat

A short cycling problem could indicate a failing thermostat battery, or that the thermostat was installed in direct sunlight or next to a heat register, where the temperature spikes can confuse it. You can try changing the battery on your own, although you’ll need to consult a technician if you need to move the thermostat to another location, or if your thermostat can’t be fixed and needs to be replaced. If you suspect the thermostat is faulty and might need replacing, you should ask your HVAC contractor to send someone to your home to exam it.

#3 Check the furnace’s blower

A burned-out blower could be the cause of the short cycling. The way to check for this is to hold your hand next to a heat register, and if air flow is super-low or nonexistent, it means the furnace is running but the blower is not.

A burned-out blower fan could be yet another indication (and an expensive one, at that) that your air filters are dirty and need more frequent changing.

Want a Foolproof Solution? Call Rheem Pro Partner

By following these tips, you should be able to solve your short cycling problem in most cases. But if you can’t, please don’t hesitate to contact Rheem Pro Partner right away. We’ll dispatch one of our top technicians to your home to inspect your HVAC system and diagnose the difficulty, and to make a recommendation on how to resolve the situation once and for all. In Colorado and Wyoming, when your HVAC equipment is malfunctioning you can always count on Rheem to help you out.