Question about Heating & Cooling
I have a question; We have a Bryant 80Plus furnace in the new house we just bought. Problem is that it sometimes locks out after 3 'misfires' - meaning it goes through the cycles to start up but then shuts off. Sometimes it starts right up, sometimes it needs 2 tries and sometimes it locks out after 3 failed tries. After 3 failed tries I usually turn the power on the furnace off and on. After that it fires right up without any problems. Guys on a HVAC message board told me it could be a faulty flame sensor. I cleaned the flame sensor with sandpaper and it seemed to run better for a while. Now the problem is resurfacing. I measured the flame sensor and it measured 5.2 microamps In the furnace manual it says that value should be 5.0 minimum. Since the measurement is so close over the minimum I wonder if sometimes the value is lower than the 5.0 and it doesn't start because of that. What do you think? Is it a faulty flame sensor or do the burners need a cleaning, or something else you can think of? In general, do flame sensors ever go bad or can they always be cleaned? I also heard that cleaning them with sandpaper is not good and can result in problems. Thanks for your time. I appreciate it very much.
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Posted on Jan 02, 2017
The two most common reasons I have found for this are listed below. You have already addressed the third one.
1) Grounding issue. This can be difficult to find but easy to diagnose. Try using a volt meter or even just a piece of wire. Touch one end to an unpainted surface of the interior furnace cabinet and the other end to the sheet metal plenum or other ground. If the symptoms go away then you have diagnosed the problem and need to find the faulty ground.
2) Pressure in the flu. Check to make sure that the flu vent pipe is not clogged or even partially filled with debris. The small rubber hose that connects to the switch from the inducer blower motor may be clogged. Also check the orifice on the inducer motor side. You can clear this with a paper clip. Water (condensation) in the inducer motor housing or pressure switch can cause a failure too. Rarely is the pressure switch itself bad. This usually will only happen if it has been physically damaged or soaked. Best of luck.
Posted on Jan 29, 2009
First when it goes out again, locate the furnace and look thru a small viewing port to see if there is a light blinking, count the number of blinks. Then look at the wiring diagram for a diagnostic code chart. This will give you a strart of where to look.
Posted on Oct 17, 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
SOURCE: Won't ignite
There is a diagnostic light on this model that will bling an error code on the circuit board. Without removing a panel, look for a small viewing port and a blinking light. Once you have found it, look on the wiring diagram for a error code chart. This will give you a starting point. If you are getting glow from the igniter but the gas valve is not opening, you could have a bad igniter (not producing enough heat to trigger the sensor). There may be an issue with gas getting to the gas valve as moyerboy2 mentioned. The gas valve could be turned off or restriction in the gas line. Check all shut-offs and your tank if propane. Check all electrical connections at the gas valve and follow the wires back to the circuit board. Tap on the gas valve when the igniter glows, maybe something is blocking the flow of gas. Hope this helps.
Posted on Dec 21, 2009
I take it this is a forced air heater,if so, ther is a relay and thermal switchs involved plus possible a sail switch in the fan housing, check circuits, oil fan motor bearings
Posted on Jan 31, 2010
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