(Nordyne/Miller G3RA)-I have a furnace HSI(glow plug) that will ignite and burn until it gets too hot and shuts down. As soon as the furnace shuts down the blower starts to circulate air. The blower circulating air cools the furnace and it reignites.Shortly after the furnace ignites the blower stops circulating air the furnace overheats and shuts down again.The cycle continues until the house reaches the thermostat setting. What temp sensor controls the blower?

Actually the problem could be with the circuit board or the fan and limit switch if so equipped. The info I have for the G3 series says that it has a circuit board in the unit for controlling ignition and the blower. The blower is controlled in a timed fashion and what is happening is the board is not telling the blower to turn during normal operation. When the unit overheats it shuts off causing the board to go into safety condition and bringing the blower on to disapate the heat. Look in your unit to see if it contains a circuit board. It might be located in the blower compartment.


Note from the service manual.

Abnormal conditions: If a limit opens during
operation, the inducer and circulating air blower
continue to operate. The gas valve is deenergized
immediately. The blowers continue
to operate until the limit closes. When the limit
closes the inducer blower is de-energized
immediately. The circulating air blower continues
to operate for the specified delay (factory

Set at 120 seconds).

My unit has both a blower and ignition control ctk boards. Robert Shaw 9248(Ignition control)
Thank you in advance

Is the control board showing any flashed on the trouble indicator lite?
If so how many flashes or blinks and then look on the back of the blower door at the diagram and post what the blink legend says.

Wish I could... no such troubleshooting tool.Is there any way to test blower and/or ignition control brds

Did you check for the number of flashes on the circuit board? I am trying to narrow down the possible problem.

My particular unit doesn't have the flashing L.E.D for troublshooting However another suggestion you gave pointed me in the right direction to find the problem-What I found was a lose wire nut between the BlowerControl and the ignition control ctk brds. Thanks a 1,000,000 $

The good thing is you have it running again. Happy New Year.