On a brand new oil furnace the burner works fine but the what seems to be a 2speed blower will not start. The limit switch shuts the furnace down after heat rises. It resets after it cools down. Restarts but still no blower. When I bypass the motor relay the blower will spin fine. Same with the delay switch. I ordered replacements for those switches and will try that. But I Am wondering if the limit switch could be at fault? or is there any other link in the blower circuit that might be causing this? It's a new appliance. The plenum and ductwork are open and free. I checked the wiring diagram and all wires are plugged in where they need be. I'd appreciate your help.



  • 2
    If bit is a brand new furnace call the installing contractor and have him fix the problem. – d.george Sep 24 '17 at 10:46
  • You should check carefully if the furnace control board is setup for separate control of the fan/blower by the thermostat. If so then there is typically a wire in the thermostat cable specifically for that purpose (often the G terminals). On units where the furnace provides fan control when the heat demand is signaled and generates its own delay there may still be a G wire that ORs into the fan control circuit so that the thermostat can support a FAN only mode of operation. – Michael Karas Sep 24 '17 at 16:00
  • Thanks for your help. It may well be the thermostat connection that's causing this. The old furnace (which I installed 30 yrs ago) had only two T terminals fora two wire Thermostat. The new furnace has a terminal board on the primary control with letters, as you guessed. So I may need a new upto date thermostat. I called a pro to help me out...I installed the furnace, – Emgee Sep 25 '17 at 20:23

Unless you have a diagram of the circuit good advice is difficult to impossible. Somewhere in the control circuit there must be a fault. It could be the coil of a relay or a lose wire or anything.

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