Manual Reset Flame Rollout switch is opening at the end of each heating cycle.

[Atlantician]

I went to a customer's house two nights ago on a service call, and found that the Flame Rollout Switch in the burner compartment in their gas furnace had opened. I reset it, and cleaned the burners and the flame sensor thinking that maybe they were getting some delayed ignition to cause the problem. I checked to make sure there were no obstructions at the vent terminations. The customer called me last night and told me that switch is opening at the end of each heating cycle now...she manually resets it (I showed her what I had done when I was there). Does anyone have any ideas as to some kind of likely diagnosis when I go back later today to reassess the problem? Its a Dependable 92 furnace...I think thats a York.
Another thing...the ventor motor seems ok, and if it wasn't, the furnace would be shutting down on an open pressure switch. I guess it could be shutting down on the pressure switch after a period of time, and then opening up the Flame Rollout switch as well from excessive heat build up.
Maybe there is a crack in the heat exchanger, allowing the furnace blower fan to effect the combustion and venting process, thus triggering the Flame roll out switch. Any ideas?

[Admin]

That's a Goodman furnace I think.  The Goodman model GHPN is pre Amana and had alot of heat exchanger failure. It sounds like a heat exchanger crack or a secondary heat exchanger blockage.  I would do a flue gas analysis.  Sometimes there's a problem with the venting termination that might cause the flue gases to recirculate into the intake and open the roll-out switch.

To test for cracks using a combustion analyzer, simply watch the O2/CO2 readings and the CO reading when the blower comes on, usually several minutes after the burners ignite.

Typically, the O2/CO2 or CO readings will stabilize within 30 to 60 seconds after ignition. If a crack is present, when the blower energizes, air (at 20.9 percent O2) may be blown through the crack in sufficient quantities to raise the O2 or decrease the CO2 reading on the combustion analyzer.

You're right, if the ventor motor stopped the pressure switch would open, but I have never seen residual heat trip the roll out switch under those conditions.

[harshal]

HI I THINK ADMIN IS RIGHT.USUALLY ITS THE HEAT EXCHANGE PRIMARY/SECONDARY.SOMETIMES ITS REALLY EASY TO FIND THE CRACK IN THE PRIMARY OTHERWISE IT COULD BE DIFFICULT.I DISCONNECT THE VENTOR MOTOR N PULL OUT ONE OF THE LIMIT WIRE TO ACTIVATE THE BLOWER.THEN SHUTTING OFF GAS AT THE GAS VLV N DO THE MATCH TEST,SO IF THERE IS ANY CRACK YOU CAN SEE YOUR MATCH FLICKERING TOO MUCH.ALSO AFTER SHUTTING POWER OFF YOU CAN REMOVE THE PRIMARY LIMIT N CHECK FOR THE CRACK AROUND THE RINGS OR MISSING THE RINGS.STILL U CANT FIND IT THAN I WOULD TRY TO SEE FROM THE TOP OF THE PLENUM AFTR REMOVING SOME DUCT WORK/A-COIL.MOST OF TIME U ABLE TO FIND THE CRACK IN THE PRIMARY HEX WITH SOME PRACTICE IN THE GOODMAN FURNACE.IF ITS CRACK THAN ONLY OPTIONS WOULD BE TO REPLACE TH FURNACE OR HEX.

[Admin]

That sounds like a great way to test.  I've never thought of doing the match test like that.  I don't see many furnaces over 2 years old these days but I'll try that out next time I suspect a crack.

[gassyass]

After you've checked the heat exchanger,if its ok,check to make sure its not overfired. You might also want to check the vent termination. If its facing north or north-west,the wind might just be enough to trip the switch. Also,make sure there isn't any sags in you venting causing a small restriction in the pipe. Water will get trapped in the pipe instead of draining back. Also check your condensate hoses and drain are clear.  Good Luck.

[Gary D]

On all York Furnace ,you must vent with long radius elbow. or you will have pressure switch probelm

[walker]

On all York Furnace ,you must vent with long radius elbow. or you will have pressure switch probelm

i think he is talking about the rollout switch tripping.

I would check for plugged secondary and/or cracks in the heat exchanger after the manifold pressure had been checked, In my experience those are the only things that will cause a roll out to trip. 

Also I would never show/advise a customer to reset their flame rollout, its a manual reset switch for a reason and if its tripping its likely something serious is going on with the furnace.

[3450BB]

I agree that you should inspect the heat exchanger. The heat exchanger gallery would be of great assistance to you.