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Short Cycling

Jim258 Member Posts: 1
I have oil heat with two zones, an upstairs zone and the first level zone. The upstairs zone I believe is "short cycling" from what I have read. When the heat (forced hot air) kicks on, it runs for approximately 10 seconds, stops and starts up again about ten seconds later. This happens about four to five time and then the heat eventually stays on until the desired temp is reached.

Is this considered short cycling? Can anyone provide any solutions if this is the case?



  • billtwocase
    billtwocase Member Posts: 2,385
    edited November 2011
    what thermostat

    do you have? Sounds like an anticipator, or CPH setting issue. If you have an old round Honeywell that is not leveled/calibrated, and has the right anticipator setting to match the zone valves, it will be the culprit. Digitals have cycles per hour settings as well
  • chapchap70
    chapchap70 Member Posts: 139
    edited November 2011
    Could be normal?

    I know this question was asked a couple of weeks ago but maybe the original poster may get an email alert. 

    Do the ducts in this zone pass through unheated space?

    From what you describe, it seems that the blower is turning on and off a few times but the oil burner should stay running through this.  This would not be short cycling of the oil burner which I believe is your concern.

    I do not work on furnaces that much but my understanding is that when a thermostat calls for heat, it turns the oil burner on and the burner heats the heat exchanger to a minimum setting.  The fan and limit control would then turn the blower on and force warm air through the ducts.  The return air would be cold enough to lower the temperature by the fan and limit control below the minimum setting which shuts the blower off.  The burner would continue to run while the air warms back up for the control to turn the blower back on.  This happens a few times until eventually, the warm air that initially started in the supply duct works its way into the return and the temperature is normalized.  The burner would stay on until either the thermostat shuts it off or the fan and limit control shuts it off on high limit.  The blower would stay running until the duct temperature falls below the fan (or low) setting.
  • mark schofield
    mark schofield Member Posts: 153
    return air

    chapchao70 has a good point. could you possibly close the returns upstairs but leave the doors open to the downstairs which would temper the return air and allow for circulation. if the blower stays on then you would at least know what the reason is. I think on the limit switch on the furnace there are three settings. High limit, on , and off. Maybe the "off" setting is set too high or too close to the "on"setting.
  • icesailor
    icesailor Member Posts: 7,265
    Short Cycling Returns:

    If that is the case, maybe look at the return duct piping and see if there is an open duct that is outside the heat envelope. Like in the crawl space or somewhere not so easily accessible.
  • billtwocase
    billtwocase Member Posts: 2,385
    need more info

    What make/model furnace do you have? Has it been underfired recently? Could be a bad or improperly adjusted fan limit control, or delay relay. Too many could be's here
This discussion has been closed.