My modine hot dawg furnace keeps popping the reset on the upper flame roll out switch,why?i've swapped the upper and lower roll out switches to determine if the switch was bad,but the upper pops regar

Sound diagnostics Henry. If there are numbers on the relay you could source one and solder it to the board.

not reading a steady flame. Clean the flame sensor with sandpaper may help but if not call a professional.

The switch you are talking about is called a roll-out or klixon high temperature limit switch. The over heating can due to a clogged flue vent, over firing from gas pressure being to high, etc. More information is needed like the model number, age, etc.

Turn power off & on again. Watch to see if it cycles...it could be the hot surface igniter if you don't see it turn bright orange. If it goes straight to blowing cold air, then normally it is a limit switch open- mostly manual reset - thermal disc-located around flame rollout.

bad flame sensor

that sounds like the limit look for a little round thing with two wires with a button between the wires push it to reset it but there could be several of them even one buy the blower motor there is also a high limit in the center of the furnace all you see is two wires if that one is out you have to remove it two screws then just drop it on the floor it will free the numeral bymetal inside put it back on and you should begood

code 33 LIMIT OR FLAME ROLL-OUT SWITCH IS OPEN - If open longer than three
minutes, code changes to #13. Flame roll-out switch requires manual reset.
Check for: - Dirty filter or restricted duct system. - Loose blower wheel.
- Defective blower motor or capacitor. - Defective switch or connections.
- Inadequate combustion air supply (Flame Roll-out Switch or fuse link open).
- Open Flame Roll-out switch, or fuse link. Manual reset or replace.

Roll out switches are sometime wired together with limits. Lack of air flow. Limits reset themselves and roll outs have to be manually reseted. Could be dirty blower,a.c. coil on furnace, or filter.

Roll out flames are a safety device on a furnace. On the furnace back up under where your burners are located, you will see a switch with a manual reset button on it. What is happening is the flames have rolled out further than they should have at one point during its cycle, and tripped this switch to keep the flames from burning the wiring and what ever it might reach.It is one of many safety's on you're furnace.Reset this switch, like I said, it would be where the flames would come out a little to far. Sometimes they will trip if you get a gust of wind down the flue pipe from the roof. Or, if the burners are getting plugged up with black soot.Check this also.Until the switch is reset, the burners will not come on. You should have no problem finding it, mounted just at the end and above the burners. Walk out side and make sure your flew cap is in place. I have found birds nesting in flew pipes that will cause this.Reset it and watch it for awhile to see how it burns.Don't worry, as that is why the switch is there, for you're safety. I am sorry for such a long solution, but it is called for on this problem. Please let me know how it turns out.
Sincerely, Shastalaker7

I am providing some information, but I encourage you to have a furnace technician look at your furnace. The reason is; the limit switch trips when there is a problem that may present a fire or combustion hazard. I've seen these switches go bad, but not very often. Usually they are tripping because the plenum is sooted up and excessive heat builds in the combustion chamber. This is common in older furnaces that have pilot flames- the flame runs all year and soot deposits in the plenum, plugging the air flow through the combustion chamber after years of use.

The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position or the limit control switch needs adjustment. Check the thermostat first. If the blower control has been set to ON, change it to AUTO; if the blower control is already on AUTO, the limit switch needs adjusting.

To adjust the switch, remove the control's cover. Under it is a toothed dial with one side marked LIMIT; don't touch this side. The other side of the control is marked FAN. There are two pointers on the fan side; the blower goes on at the upper pointer setting and turns off at the lower pointer setting. The pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.