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Posted on Jan 02, 2017
The flame rollout sensor is a rather important safety feature that ideally only trips when there's an overtemperture outside of the combustion chamber. I'd encourage you to get a better quality tech in ASAP to check for a cracked heat exchanger, gas overpressure, restricted airflow (changed the filter lately?), maybe a blocked condensate drain if this is a high efficiency furnace. If the sensor was replaced and it's still tripping, you've got a potentially dangerous overheating issue that you don't want to try to bypass.
Posted on Mar 20, 2009
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). When all else fails, check the ground connection for corrosion.
Posted on Nov 23, 2009
if you have replaced the flame sensor and it will not stay lit, the draft safety switch may be opening. It works on positive and negative pressure created by the inducer fan motor.You may have a restriction in your heat exchanger or if is a high efficiency furnace, it may not have the drain tube installed properly with a trap. The trap works just like the trap under your sink and if water isnt in the trap, the pressures can be effected enough to open the draft switch(some call it an air pressure switch)
Posted on Jan 07, 2010
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