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Hi everyone, I am new here and was hoping to get some help.

The system is hydro air, conventional boiler (oil), super store hot water heater; two air handler’s one in basement for first floor heat and A/C, other in attic for second floor heat and A/C, the system is 12 years old. Air Handlers are both: First Co. Model # 48MBXR-9HW

The problem I am having is that sometimes in "Auto" mode; the air handler blower fan doesn't always start, the thermostat calls for heat, the furnace starts and the pipes get hot. It works fine if I change the setting on the thermostat to “Fan On” mode, but then it’s on all the time. Now, I have found that if I remove the face place from the digital set back thermostat and then put it back on the air handler will come on.

The problem doesn't always happen and it seems to happen more in the mornings. Initially I suspected that the problem may be with thermostat but replacing the thermostat three times did not help.

The original 2nd floor thermostat was identical to the 1st floor thermostat. My heating guy checked out the new thermostat and it’s not the thermostat he just can’t figure it out.

Now, these are two strangest things:
1. 2nd floor heat and A/C work fine
2. 1st floor A/C works fine

So the problem is only on the heat side of the circuit on the air handler on 1st floor, what’s my problem?

Thanks