Recently, my Pane PG8DAA downflow furnace stopped delivering heat. The fan was running constantly, but the air was cold. The trouble codes were 33 which becomes 13 after a period of time. Powering off the furnace and restarting would trigger the gas ignition, but it would not stay on. After having the unit inspected professionally, the problem was determined to be poor airflow caused by clogged filters. I use 3M Filtrete filters and the technicians said it’s very common for these high grade filters to clog early and when they do it’s like having a piece of plywood in the air way. He said these kinds of filters should be checked every 30 days.
Since the trouble code pointed to the flame roll-out sensor, I thought manually resetting that would be the way I’d get the gas back on. The technician explained that if I had had a flame roll-out problem, my eyebrows would have been signed off. In other words, there would be no mistaking it. You would see the flames rolling out of the furnace.
My old furnace had a heat exchanger that had to be inspected every year for dangerous cracks. Given that the high limit switch was also a culprit, I was concerned that I might not have a similar problem and so I was glad to have the unit inspected. The tech said the newer furnaces are so pressure sensitive that cracks in the heat exchanger are very evident. You will see flames rolling out or the flame change from blue to yellow as it mixes with air leaking into the exchanger. He said he could tell just by looking at the flame that there were no cracks in the exchanger.
Here are the things I learned :
These codes can be set by a problem with the high limit switch, which shuts off the gas when the temperature in the heat exchanger exceeds the upper limit.
Symptoms: the blower fan comes on immediately after powering the furnace back on. The gas does not come on.
If you suspect this as the problem, try setting the fan from auto to on to cool the exchanger. Make sure all the vents are open. Clean or replace all the filters.
You can reset the high limit switch by tapping on the tan plate above the wires. Be careful to not touch to wires.
If the problem is the high limit switch, these are temporary measures that may provide a work-around until you can have the unit professionally inspected.
These codes may also require the limit or flame roll-out switch to be reset. The two switches are located above the three burners. If the flame “rolls out” instead of into the heat exchanger, the sensors detect the heat and shut off the gas. Manually reset the sensor by turning off the furnace and pressing the center tab down on the back, upper side, of the switch.
Or, they may mean dusty burners. Clean by using turning off the furnace and blowing compressed air into the burners. A shop-vac that can blow air can be used as well.
Ensure that there are no closed vents which would restrict air flow. Clean or replace all the filters. High grade filters like 3M Filtrete, because of their efficiency, may need to be replaced earlier than the manufacturer’s recommended 90 days. Check every 30 days.
Additionally, the flame sensor may need to be cleaned. Steel wool is best. Fine sand paper may be used, but you must remove the sand paper residue with a damp paper towel.