This sounds like a flame sensor issue
The flame sensor rod is a small thin steel rod that is straight or L shaped. It is usually located inside the furnace cabinet near the pilot igniter or the outside corners of the burner tray. Locate it, remove it, and clean it with a piece of sandpaper. Thanks!!
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This unit has three burner jets. The ignitor is positioned in front & between burners # XXXXX&2. There is a thin metal rod positioned vertically & directly in front of burner jet #3. Is this the flame sensor rod? Note: when I turned the power back on to the unit this time it cycled on and the burners burned for about 30 minutes. When the unit cycled off, I noticed the self-diagnostic panel was flashing three three flashes. The inside panel instructions indicate that this indicator = low fire pressure switch stuck open. Suggestions?
First of all yes, that is the flame sensor rod.
Second of all, is the three flash code still flashing?
not now. I recycled the power off for 30 minutes and then back on. It appears to have run through the cycle this time and the diagnostic light is solid on.
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I turned the power off to the unit last night (Friday). This morning I removed the flame sensor rod and cleaned it and the contact with a small piece of new super fine sandpaper. Thermostat is set at 67 and room temperature reading 59. After turning the power on to the unit, the unit functioned properly until the room temperature rose to 64, and then cut off temporarily, and began doing the same thing it was doing before. The diagnostic light is now flashing three times. It would appear that the unit will operate correctly for most of an initial cycle after setting for several hours with no power on, but then the on & off of the igniter and gas jets begin. I am currently surviving turning the unit on for about 30-45 minutes, and then when the unit powers itself down I turn the power off for 3-4 hours. Any more suggestions?
It sounds like your High limit switch is opening and closing. The high limit switch is a rectangular device that is located inside the furnace cabinet and sits on the back panel wall. It has two wires attached to it. Locate it and remove the two wires and attach them together. Attach them metal to metal very good and call for heat. See if the heater runs with no interruptions.
Let me know what happens.
This did not help. Same sequence occurred. Again, when the unit begins to cycle up and back down, the diagnostic panel flashes THREE times. When I first turn the power back on and it runs normally, the diagnostic light is steady ON. Is it normal for there to be some water in the variable speed circulator (I think that is what it is called). When it first comes on (low RPMs), you can here the water sloshing. I verified that the drain is working. anymore suggestions.
Do you see any way that you can drain this water?
If so, do it.
Water is drained. Unit will run normally until it gets temperature up to the thermostat setting. It then begins the on, then off cycle of the igniter followed by a short ignition of the burners (30 seconds) over & over. The diagnostic light is flashing three lights. The inside panel instructions indicate that this indicator = low fire pressure switch stuck open. Suggestions?
The inducer Fan Motor is located inside the furnace cabinet and is connected to the flue vent pipes. It has a rubber hose attached to it that connects to a round pressure switch.
Remove the rubber hose and blow through it to make sure that it is clear. Also inspect it to make sure there are no leaks or tares. Then use a paper clip to clean out the connection at the inducer fan motor.
Call for heat and see if the problem still occurs.
The rubber hoses were clear.
The unit still will run for about 15 minutes (not a full cycle) before cutting out. During the initial cycle, I believe the main blower is only running at normal first stage and never ramps up to the second stage. When the unit kicks out the diagnostic light is now flashing one light, then flashes three lights. One flash = system cutout (too many recycles)
Three flashes = low fire pressure switch stuck open. Any more suggestions?
I would advise you to call a technician out to complete troubleshooting.