The blower on my Dayton furnace runs but there is no flame/ignition. Just blows unheated air. It continues to run regardless of whether the thermostat is calling for heat or not. Anyone have any ideas?

If the fan comes on first, then the flame ignites, it USUALLY indicates there is a problem in the ignition process of the furnace. Most new manufacturers have the adjustable 'time off' sequence for the blower, and most initiate a call for the blower to run within a pre-determined amount of time AFTER a call for heat has been established. ALSO, and this is where I think the problem is, the ignition sequence starts immediately upon a call for heat. If there is a heat ignition failure, it will attempt a restart. USUALLY, they allow 5 restarts within a certain timeframe then the circuit board locks out the heat sequence until it is reset by cycling the power or cycling the thermostat manually.

What I think is happening with yours it that your ignition sequence is experiencing a 'flame failure' upon a call for heat....then it re-establishes the ignition sequence, which takes another 30 to 45 seconds. During this time, the blower automatically starts (because the allotted time has expired) and blows COLD air because of the initial flame failure. In the meantime the ignition sequence establishes a flame on the second or possibly the third try and then you feel the warm air.

IF this is the case, ultimately what will happen is that the furnace will continue to experience 'flame failure' and eventually fail to the point of 'flame failure lockout' and you will have no heat, but the fan could possibly run continuously.

At any rate, without being able to be there to troubleshoot and test components physically, this is just a calculated and reasonably reasonable guess. What it is telling you is that you probably need to contact a reputable, reliable service organization to give your furnace a good going over before it lets you down on a good cooooold night!!!

I hope this helps you understand the basics of what happens within the system and bear in mind, this is a 'generic' sequence and possibly NOT the exact sequence of your particular furnace.

If the sensor knocks the unit off and the the fan keeps blowing without a flame ,the limit (the sensor is a limit comptroller that turns off flame @ a set temp and allows the fan to run until the heat exchanger cools to @ set temp) has out lived its lifetime and needs to be replaced.the button is a manual reset that once reset would allow the unit to continue to run flame and blower at the same time after having been set once, if it is an ongoing problem and needs to be reset more than once then replace the limit control (sensor) in kind. (With the same mode and set-points for the limits)

Fan control could be on summer switch. or af control not working keeping fun running

sounds like the furnace control (low voltage) circuit is open, or in other words you either have a fuse blown or a limit switch that needs to be reset. Most newer furnaces have a small knife like fuse, usually 3 or 5 amp located directly on the circuit board. Limit switches that have a manual reset are usually located in the fire box just above the burner. There may even be a limit switch located on the blower assembly. If you fuse was blown, you may need to find out what caused the short in the circuit or it will do it again. If the limit switch was tripped, you need to turn the furnace back on and watch the flame to see if there is "roll out". It it continues to trip or blow fuses you need to have the unit serviced.

I'm not sure whether this is a gas unit or not. With many gas heaters, the blower comes on when the heat exchanger gets hot enough and goes off once the heat exchanger cools. Other things are happening before the blower goes on. The blower is normally controlled by a "fan control thermostat". This stat actuates the blower when the furnace is hot enough so that cold air is not being blown around and allows the blower to run until the furnace cools enough to get out the remaining heat after the flame shuts off but not so long to again allow cool air to blow around. If this fan control is malfunctioning, you will get erratic runs from the blower or the blower may not run at all or run long or continuously. The fan control is the first thing to check.
Gary

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, Dirty Air Filter), 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).

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).

Bad fan switch. It may also be called a fan limit switch. If your furnace is less than 5 years old, the switch is part of the circuit board and you will need to replace the board.

Flip the lower panel over and look for a wiring diagram. On that diagram there will be a diagnostic chart. Let me know what 5 blinks represent. Then I want you to read on.

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).

Make sure a back draft in the flue is not happening. Wind can blow it out until the flue heats up. The flame sensor may not be close enough to the burner flame. It may be weak and need to be replaced or if its an optical one it may be dirty and not see the flame very well. Its not wasting much gas but it puts extra wear and tear on the gas controls, is noisy, and, as you said, blows cold drafty air. A gas control system that has issues of any kind is not real safe. It needs to get fixed.