Troubleshooting a Short Cycling Furnace

A properly working furnace is a necessity to keep the home comfortably warm during winters. However, a furnace may malfunction or develop problems after a period of considerable inactivity during the warmer months. It usually happens when a homeowner fails to invest in annual furnace maintenance right before the beginning of the cold season. 

A common and annoying furnace issue that homeowners often encounter is short cycling or overheating. Short cycling is a situation when a furnace frequently turns on and off, and the time between the on and off cycle is lower than usual, preventing it from effectively heating your home to the correct temperature on the thermostat.  

Let’s look at a few reasons that cause a furnace to short cycle and ways to fix them to get the unit up and running again:

Incorrectly sized furnace

When short cycling occurs soon after furnace installation, it may mean that the unit is too big for the home’s size. Oversized furnaces offer quick but uneven heat distribution. It causes the furnace to short cycle to maintain steady home temperatures. Unusually high utility bills and drastic temperature differences throughout the home indicate an issue with the furnace size. Consider replacing the furnace with a smaller unit to stop short cycling. 

Thermostat issues

A wrongly-positioned thermostat may cause the furnace to turn off frequently. If the thermostat is located in direct sunlight, too close to vents, or near other heat sources, it gets warm quickly and reaches the set temperatures before the rest of the house, signaling the furnace to turn off prematurely. It usually happens with DIY or unprofessional installations. Move the thermostat away from heat sources. 

A broken or malfunctioning thermostat also causes short cycling. Check the batteries, ensure it is on heat mode, or test it for other common issues to stop short cycling.

Dirty or clogged furnace filters

A clogged air filter is one of the most common causes of a short cycling furnace. It restricts smooth airflow to the heat exchanger, causing the furnace to overheat and inducing the high limit switch shuts the unit down. Clean or replace the dirty air filters to allow unrestricted airflow and prevent overheating.

Malfunctioning furnace parts

Issues with the furnace blower motor, heat exchanger, or flame sensor are other common reasons for short cycling. A failing or damaged blower motor, corroded flame sensor, or damaged heat exchanger may also cause the furnace to turn on and off quickly. An HVAC professional can inspect, clean, repair, or replace the furnace parts to reinstate proper functioning. 

Clogged exhaust vent

Blockages in exhaust vents due to snow, ice, and debris, gas build-up inside the furnace overheats it, causing it to shut down repeatedly. The gases may not find an escape due to the blocked vent. It is potentially dangerous as it may release hazardous carbon monoxide gas into the home through the vent. Keep the flue free from any obstructions and install a carbon monoxide detector. 

Is your furnace giving problems?

Short cycling is dangerous for the furnace. If not addressed on time, it puts strain on the system, leading to frequent breakdowns, expensive repairs, uneven temperatures, increased energy bills, and reduced system lifespan. If you are stuck with short cycling and cannot identify the root cause, give the local HVAC contractor a call to examine and stop a furnace from short cycling as soon as possible.

When you need heating or refrigeration service, maintenance or repair, call us at Affordable Comfort A/C and Heating 602-574-1205.