My AC tech, via text, had me remove the float in the air handler to see if it would come on and stay on, it did not. Furnace Keeps Turning On and Off Repeatedly? Thermostats near heat sources or in direct sunlight can warm too quickly, signaling your furnace to shut off. Source. This sends the incorrect message to your furnace so your furnace shuts off. What could be the problem? This is not normal behavior and the problem is unlikely to clear up on its own. Favorite Answer. Dirty air filters are a common cause of furnace cycling problems. AC , Furnace, and Blower not turning on w/ thermostat set to Auto or On. 4. That’s no good. Its not like it turns on or off for minutes at a time, its almost constantly switching on and off, it will switch on and then before it has time to even get to the full speed setting it would turn off again. Recently I have noticed that my blower from my furnace has been turning on and off randomly. We use cookies to give you the best possible experience on our website. Solution: Replace the air filter. Why is My Furnace Turning On and Off: Common Problems and Solutions Problem: Dirty Air Filter. Step 1: Locate your fan limit switch. Replacing the capacitor and cleaning the filter should be enough to get your furnace up and running again without the annoying humming sound. Diagnose furnace blower problems: this article describes what to check if the warm air heating blower fan cycles on and off after the call for heat has stopped, that is after the room thermostat has been satisfied. Furnace turns on after call for heat has been satisfied: This article describes what to check if the warm air heating blower fan cycles on and off after the call for heat has stopped, that is after the room thermostat has been satisfied.. A dirty air filter restricts air from getting into your furnace. Step 1 Replace your "furnace limit switch." If it does, the Nest is the problem. If your furnace is coming on and isn't turning off, you need to investigate the issue, as it could end up costing you excess money on your utility bill at the end of the month. Answer Save. … Along this same vein, another sign that you might need a new capacitor comes when your blower slows down too much. Furnaces are calibrated to turn on and off based strictly on changes in indoor air temperature. To help keep your furnace from constantly turning on and off, make sure that you change the air filter at the start of each new season and check it monthly. As a temporary solution, while I waited for my replacement, I hooked my W1 (furnace) to Y1 (cooling) and turned the temp down. This is most common cause of short cycling. First, try turning the furnace power switch on and off. Your fan limit switch is located just under your furnace hood and is in charge of telling your furnace blower when to come on. The blower won't come on for 30-45 minutes after the AC has been turned off, but after that it seems to turn back on fine. We replaced the air filter and thermostat, same issue. My furnace keeps turning on every 8 minutes, runs for 3 minutes and shuts off for 8 minutes again. See if the furnace works. The AC unit outside would shut off when the set temp was reached, but the fan inside continued to blow. Blower on furnace keeps turning off and on when the furnace isn't calling for heat. ... Blower does not come on. This is a safety feature that will turn your furnace off. Problem: Furnace Short Cycling. Some other possibilities (if applicable) would be: a blocked/clogged flue, a dirty flame sensor, or a faulty furnace blower motor (very uncommon). So it shuts off the gas valve. Your flame sensor is what properly gauges how much gas is going to your furnace. This pattern of functioning is called short cycling, and it is a sign of trouble that you cannot afford to ignore. Answer: Being able to interface the Aprilaire humidifiers to turn off and on with the furnace blower or gas would depend on whether you have “HUM” (humidifier) hookups on your furnace’s control board. Normally, this switch should allow the furnace burners to warm up completely before turning the fan on and should keep the fan running just until the burners cool off slightly (to prevent damage or overheating). Some basic furnace troubleshooting will help you determine if the issue is something you can fix or something that requires expert attention. But lately it's been turning on and off. After the furnace stops running the fan/blower runs as usual. But sometimes, furnaces will begin turning on and off too rapidly to be responding to temperature variations. Drain line appears to be clog free as water is dripping from it. Bypass the Nest by turning off the power to the furnace, attach Rc and W1 together, restore power. If this doesn’t work, turn off the power and gas supply to the furnace. Lv 5. This is a repair that needs to be handled by professionals. why my furnace fan keeps running - Furnace fan runs constantly nest thermostat furnace fan runs constantly why does my furnace fan run constantly The part(s) or … Turn the blower motor OFF (when the heat exchanger drops in temperature after a heating cycle) Turn the furnace blowers off (when the heat exchanger hits dangerously high temperatures) That said, if your furnace fan limit switch is damaged or has been tampered with, it might allow the fan to run even after the heat exchanger has cooled off. Here's Why Your Furnace Keeps Turning Off. Relevance. [ 20 Answers ] Here's my issue. The Blower motor on my AC unit turns off at random times while the outside unit continues to run which is causing the coil to freeze up. Let’s take a look at the most common causes for a furnace that won’t shut off: For other common problems, see: Furnace Keeps Turning On and Off … Gas and Oil Home Heating Furnaces - Furnace keeps turning on and off - So my furnace control board shorted out a few weeks ago so I replaced it. Flame Sensor. Question: My humidifier runs all the time, even when the furnace is off. 10 Reasons Your AC Keeps Turning On and Off & How to Fix It. This is a very common problem that if not diagnosed and corrected immediately could result in higher utility bills and major furnace repairs. - AC … gas forced hot air furnace - Answered by a verified Home Improvement Expert. I cannot turn on either my AC, Furnace, or Blower from the thermostat. The fan will turn on as usual then about a minute later it will turn on for approximately 30 seconds, turn off for one or two minutes, then back on for 30 seconds. It runs good heat. You should also test your thermostat to ensure it’s working correctly. The fan limit switch is responsible for turning the blower on and off at the appropriate times. Bit of background: The furnace blower originally did not not turn off at all (or if it did, very rarely did so), even when set temps were reached or when the system was off (fan setting is set to auto, not on). The Guide to Troubleshooting a Short-Cycling Furnace. Why is My Furnace Leaking Water? These 90% furnaces may start-up and run fine at the beginning of the season as the blockage absorbs the condensation and may even drain with no negative results. 2 Answers. The term we use to describe a furnace that keeps turning on and off is “Short Cycling.” This problem originates from inside the heating system. There are 3 common reasons why a furnace keeps turning on and off: 1) Dirty air filter. my furnace keeps turning on and off before it runs, any help? Same issue, even when the furnace is off is responsible for turning the blower to slow.. 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