Nordine (Miller) Oil Furnace cycles MANY times on cool down

[wwcordes]

I have a newer Miller Oil Furnace (now Nordine), Model # CMF2-80(PO), S# cma06/20058. It works great... once the burner shuts off, the fan continues to run until it reaches the low limit setpoint - but then it will cycle the circulating fan on and off between 9 to 12 times before it shuts down completely... takes about 1.5 - 2 minutes of this annoying cycling to turn off completely. The blue limit (electronic) setpoint label says F115-20F (part # 626552). I'll assume it takes the heat exchanger temperature down to 115F, with a 5 degree variance? Is this a flaw in the Miller design or do I have a bad limit switch or ? Would a different switch with a greater variance stop this problem? Walter Cordes, Cedarville Michigan.

[Robert]

Hi Walter,


That is not a limit, it is the fan switch.


It kicks the blower in at 115* and then after burner shut down, keeps blower running until chamber cools to 95*.


This could be a bad switch or a problem in heat exchanger not allowing heat to dissipate or air getting across the switch for some reason.


Due to possibility of a safety issue, would be best to have an hvac tech check it out.


Miller is made/owned by Nordyne.




Thanks,
Robert