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Furnace blower fan problem

Hi Guys
Got a problem that just started to appear lately.

Typical operation - thermostat turns on, flame turns on, fan kicks in.
Problem now is, that the fan will run for about 2 minutes or so then shut down. This will happen two or three times before it remains on and continue to run until the set temp. is reached. I never lose the flame during this time. I have also noticed that this problem only seems to occur in the morning on initial start up. It seems to function normally once it has ''warmed up'' so to speak.
The thermostat (Honeywell) has been replaced for observation - no change.
Thoughts on where to go next? relays, timers, blower fan cap?

Model: Rheem furnace RGDA-100E-GR (100,000 BTU, natural gas)

Frank P

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  • Heating & Co... Master
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Hi check out the fan control switch could be dirty itsounds like this is nit cutting to let fan run also check setting fan off fan on , temp rise and fall

Posted on Feb 06, 2010

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Can not get fan on to turn on. All else fine. heat only furnace. No air conditioning...only air circulation.I used to set it on "Cool" and "Fan On"and get air to circulate. Do I need new thermostat?


Since you have two thermostats that operate the heating unit and the fan, and the fact that neither will turn the blower on, I would suspect the furnace/ air handler. Turn the thermostat to heat and see if the heat and the fan comes on, if it does operate normally in heat, the fan relay or the high speed on the blower is most likely the culprit. (If the furnace is equipped with a circuit board, the fan relay is integral to the board, if it an older furnace it has a separate fan relay). If it does not operate normally in the heating mode, verify power to the furnace, see if the flame comes on, if it does: the fan motor, circuit board or the fan relay are most likely the cause. hope this helps!

Jul 20, 2015 | Heating & Cooling

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I have a Rheem Furance that has turned off. Just a few hours ago the main fan turned off. The Furnace doesnm't light even the draft fan does turn on and then the main fan blower motor turns on. I can hear...


You will need to reset the furnace by turning the power off to it. Then as the furnace tries to light, watch the LED for blinking. Hopefully it will give a code other than 1. Try checking the air filter for blockage, make sure all hoses are free of moisture and any drains are not blocked. Check the air intake and exhaust pipe for sags where water could block it.

The sequence of operation is this:
Thermostat calls for heat, the LED may blink telling you it registers the call. The inducer (exhaust) blower starts closing contacts in the pressure switch (small disc shaped thing), the igniter glows orange (seen thru a small window high up on furnace front), gas valve opens allowing main burner to light, flame travels to all other burners, flame rod senses flame within a few seconds and keeps gas on. Room air blower starts within 90 seconds.

Any deviation or delay in this sequence and it goes into lock-out.

Jan 22, 2011 | Heating & Cooling

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Hi i hope you can help. I have a high effeciency furnace and the burners keep turning off.


On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

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1 Answer

Thermostat calls and from time to time won't ignite


I would first look at any wire connections both at the furnace and the thermostat. Then I would replace the thermostat. Check the units control board when it does not start for an error code. There should be a small viewing port to look into the furnace cabinet to see the control board.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

Feb 12, 2010 | Goodman Heating & Cooling

1 Answer

My furnace will not shut off on auto. the fan will not run when switched to on. what should I check?


Some new furnaces have a feature that when it has an issue, it starts the room air blower until you reset the thermostat or kill power to the furnace. Not knowing what you have for a system I can offer you only how a furnace works and what you could look for "generically".

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

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1 Answer

The furnace send signal to the fan in about 30 seconds, now this fan is set in auto from my termostat, my problem is the fan is starting slowly and some time it don't start, but if I use the option manual...


Depending on the model of the furnace, the blower is either a 2 or 3 speed. When the furnace operates in heating mode with the thermostat in the auto position, the furnace starts the fan when the furnace reaches a specific temperature or after a set time delay, but it operates the fan in low or med low speed on heat mode, when you put the thermostat fan switch in the "ON" position, the furnace operates the fan in "HI" speed, the same speed used for cooling mode. You may have a blower moter that is starting to short. I would recommend having a professional replace the motor before now before it becomes an emergency in the middle of the night during a cold spell.

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2 Answers

Blower turns on when stat calls for heat but manifold is not being ignited (do not hear gas valve even trying to release gas). No spark either. Could it be insufficent gas pressure?


Here is the ignition sequence for a spark ignited furnace. This will help you understand what is happening/not happening.

Thermostat calls for heat.

draft inducer motor (DIM) starts drawing draft through heat exchanger.

Pressure switch detects proper operation of DIM, and sends signal to board to begin ignition.
(it detects negative pressure)

Ignitor starts ignition attempt and gas valve sends gas to burners.

Upon ignition, flame sensor detects flame and sends signal to board stopping ignition sequence and continuing gas flow for heat mode operation until thermostat is satisfied.

During this sequence the blower motor is brought on, and by using a series of temperature limit switches, the system assures that the unit is operating properly.
(If the blower is not operating, or the airflow is inadequate, the heat exchanger will overheat and trip one or more temp limit switches.)

There is also a "rollout" switch that detects improper flame pattern "rolling out" into the controls compartment.

Now, to apply that to your situation.

If you have no spark, than the failure is happening before the gas is supposed to be flowing.

That usually means a failure at the D.I.M. Typical causes for that are a clogged flue pipe/vent, damaged/deteriorated fan blades, bad fan, or bad pressure switch.

If one of the temp limit switches or rollout switches have tripped, it will simply shut off the system.
(Some units will turn on the blower motor and shut down everything else.)

You can try resetting the unit by disconnecting power for 1 minute, and attempting a restart.

First look for any flashing LED lights. If you see any locate the wiring schematic (usually on the inside of the front panel) and look for the flash codes.

If the reset does not solve the problem, let me know what flash code you are getting, and/or let me know exactly what you see the furnace doing, in detail, after the restart.

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Carrier Weathermaker SX model 58SX060-CC Blower runs all the time


Remove all power from the furnace, it is likely the brain in the furnace is need of being reset, from the battery replacement, why did you change the battery, was there an indicator telling you to change it?

Many times just removing all the power to the furnace will do the trick with a reset, if not let me know and we will go from there, but it sounds like the main brain is confused or bad, more likely confused, so try the power removed first.

Than let me know wbwill@sbcglobal.net

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Your hot surface igniter may be bad. It may be cracked which would prevent it from starting the burner flame.

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