Why is my furnace short cycling?
Why is my furnace short cycling?
The most likely cause of short cycling is the fan limiter, which prevents fires and furnace damage by shutting the system down if the heat exchanger becomes too hot. A dirty flame sensor or damaged thermocouple will shut off the gas valve and the furnace. This prevents natural gas accumulations that could cause a fire.
When do you turn off the Furnace Fan?
So, when the switch is working correctly, your furnace fan should turn on several minutes after thermostat calls for heat and turn off several minutes after the heat cycle ends. But if the furnace fan runs continuously, regardless of whether the furnace is heating or not, your furnace fan limit switch is either:
Why does the Furnace Fan keep running during the heat cycle?
Details about these three settings are at FAN LIMIT CONTROL SETTINGS. In this common situation the furnace heat source or BURNER goes OFF then back ON DURING the HEAT CYCLE while the blower FAN KEEPS RUNNING – that is while the thermostat is continuing to call for heat.
When does a short cycle furnace turn off?
A furnace that works as it should will turn on and run until it reaches the desired temperature. After this, it will shut off while your house maintains the heat level. It will switch on once the temperatures drop, but this usually takes a while. However, a short-cycling furnace will turn on and off in quick successions.
How does the Furnace Fan limit switch work?
Your furnace fan limit switch is basically a control system that determines when the furnace blower assembly should turn on and off. The system uses a “temperature probe” to detect temperature changes inside the heat exchanger (see image below) and turns your blower on and off in response.
So, when the switch is working correctly, your furnace fan should turn on several minutes after thermostat calls for heat and turn off several minutes after the heat cycle ends. But if the furnace fan runs continuously, regardless of whether the furnace is heating or not, your furnace fan limit switch is either:
Details about these three settings are at FAN LIMIT CONTROL SETTINGS. In this common situation the furnace heat source or BURNER goes OFF then back ON DURING the HEAT CYCLE while the blower FAN KEEPS RUNNING – that is while the thermostat is continuing to call for heat.
Why does my furnace blower turn on and off all the time?
But since temperatures inside the heat exchanger should stay relatively stable when the furnace burners aren’t on, your blower fan shouldn’t be needed at all. So if your furnace blower is turning on and off when the furnace isn’t in a heat cycle, it usually means the fan limit switch is defective.
Your furnace fan limit switch is basically a control system that determines when the furnace blower assembly should turn on and off. The system uses a “temperature probe” to detect temperature changes inside the heat exchanger (see image below) and turns your blower on and off in response.