Furnace short cycling

When your furnace is short cycling (frequently turning on and off) and not reaching the desired temperature in your home, what are the possible causes? Not only does a short-cycling furnace waste energy and increase your utility bill, it can also lead to a part failure if not addressed quickly. Below I will list a few possible causes of a Furnace short cycling.

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1. Dirty filter(s)
2. Oxidation of the flame sensor
3. Plugged or partially plugged condensate drain (in high efficiency furnaces)
4. Improper temperature range
5. Dirty or malfunctioning blower motor
6. Restricted airflow (#1 above. Also, dirty blower wheel, plugged AC coil, blocked return and/or supply registers)
7. Blocked or partially blocked vent
8. Defective pressure switch
9. Defective IFC (integrated furnace control: circuit board)
10.Plugged/partially plugged burners

If your furnace is short-cycling it is best to have your system inspected by a qualified heating technician. Failure to act quickly and have the cause corrected could result in complete system failure and costly repairs, or worse. For instance, a partially plugged vent can cause the furnace to overheat and shut down on a temperature or vent limit switch. In older furnaces such as those with a standing pilot light, this condition could lead to fame roll out from the burners and carbon monoxide leaking out of the furnace.
When your furnace is short cycling it’s trying to tell you there’s a problem. Ignoring it will not make it go away. It will likely lead to additional problems and thus a more costly repair to get the unit up and running as designed.
I’ve heard far too often from Colorado Springs area homeowners who call AFTER their furnace has quit working completely, only to hear them say “Well I noticed it started acting up a few days ago but it was still running. But now it won’t come on at all”.
One example of ignoring the problem that I’ve often seen is that a furnace will begin to short-cycle due to a dirty or oxidized flame sensor. A furnace will usually heat fairly well with a marginal flame signal, but once the temperatures dip and the furnace needs to run for longer cycles to keep the house warm, it won’t be able to keep up. In this particular situation, the sensor will cause the furnace burners to light but fail to stay on thru the heating cycle. This in turn can cause the ignitor to fail due to frequent re-starts, as well as cause the temperature limit switch to fail due to overheating of the heat exchanger prior to the main blower motor coming on. When this problem is ignored it will likely lead to the homeowner having to pay for additional repairs that could have easily been avoided.
In conclusion, if your Furnace is short cycling then something is not right with it. Have it checked and serviced as soon as you notice something is amiss. Waiting even an extra day may cost you several hundred dollars more.
Basset Heating & AC 719-392-0032 Colorado Springs, Fountain and surrounding areas in El Paso county.