I have a Goodman propane-fired furnace GMS950904 CXA. Both yesterday and now today the circulator blower runs continuously but the furnace does not operate. The LED flashes six times, indicating an open in the rollout circuit. There are two rollout switches/sensors on the furnace that are stamped with L200F plus a pile of other numbers. Both times one of them (same one) tripped out (opened up). I reset the switch and things go back to normal until the next failure. I assume this a 200 deg F switch. Goodman's website was not helpful in getting a part number.

The owner's manual offers these possible causes: flame rollout, misaligned burners, blocked flue and/or air inlet pipe, failed induced draft blower, loose or improperly connected wiring, faulty rollout limit switch. These are the results of my inspection of these items: no flame rollout visible during start up or steady state run with all furnace panels in place, no indication of burner misalignment, no blockage in flue or inlet pipes at their openings outside (don't know about the rest of the piping), induced draft blower replaced 2.5 years ago, bearings are quiet, nothing wrong with the wiring that I can see. There is no melted wire insulation, carbon deposits where there shouldn't be, mouse turds, etc.

That leaves the rollout switch itself. I took both the rollout switches out of the furnace and set our kitchen oven at 180 deg F. I put the switches in the furnace for several minutes and then checked the switches. They hadn't opened up. Next up 200 deg F, still closed. I kept going up in 20 degree intervals. I had to go to 280 degrees to get the switches to open up. They both opened when I set the oven at 280. I realize this oven is not a laboratory instrument but I'm surprised there's that much of a difference between the oven and the snap action rollout switches.

We live in Massachusetts so our furnace had a summer vacation. But October has been cold so the furnace has been running for several weeks now. If I had some air blockage problem due to critters building nests in the supply or flue pipe I would have thought it would have shown up by now. So what do I check next?

 

Are these two limit switches located adjacent to the burners ---probably next to or above the burners? Describe where these switches are located.

One of them might be for something other than flame rollout.

You could have any number of possible problems which are overheating the flame rollout switches. An overfired furnace might cause such a problem.

Something is causing the flame rollout switch to overheat and open. That might just be radiant heat from the burners rather than actual flame reaching out to the front of the furnace.

You probably have something going bad that will get worse over time, with the switch opening more and more often.

I never had occasion to replace a flame rollout switch --- they just sit there and they basically never go bad.

 

This furnace has 4 inshot burner tubes arranged horizontally. Let's call the leftmost one number 1 and rightmost one number 4. The rollout switches are located between burner tubes 1 & 2 and between 3 & 4, slightly above as I recall. They both say L200F on them and they look identical. For the fun of it, I interchanged the two switches to see if the problem follows a particular switch or if stays on the left side. I will let you know.

After I interchanged the two switches I watched the furnace in operation through the viewing port on the furnace for maybe 10 minutes. I saw no indication of flame rollout. However, I felt the top of the furnace over the burner tubes and I would say the area over tube 2 was definitely hotter than the others. I tend to agree with you that the left switch between tubes 1 & 2 is getting too hot. For the furnace to be overfired I assume the gas pressure would need to be too high. I do have a pressure gauge so I could check the gas pressure. But if that was the problem then ALL the burner tubes should be oversupplied with propane, and I don't see that. What else could cause one burner tube to be burning too hot?

Thanks for your perspective on the reliability of the rollout switches. They are pretty simple devices and don't carry a lot of current so I guess it's not surprising that they rarely fail. But there's nothing like experience.

 

They rarely fail because it's rare they are called upon to act. Flame rollout is a pretty serious problem.

I remember in the past that that 95% furnace was particularly sensitive to venting.
The following is the manual for your furnace.

alpine home air/viewresource.cfm?ID=2470

A question.... how is the furnace oriented.... where are the burners ?
Can you shoot and post a picture for us ? http://www.doityourself.com/forum/el...-pictures.html

 

OK, so I interchanged the two rollout switches. The failure follows one switch. When it was on the left between burner tubes 1 & 2 it failed. Now that it's on the right between burner tubes 3 & 4 it still fails. So there is something about that switch that seems to predispose it to open up.

I was not able to post photos in the past. I will try again. In the meantime, let me try to describe the arrangement. The furnace is in a cement basement. It's located close to the back wall, facing the inside of the basement. There are 4 inshot burner tubes that are arranged horizontally. The air supply and flue pipes (3" PVC) go off to the left, make a few twists and turns to get up between two floor joists and then go out the left side of the house. The total length of piping is about 25 feet from furnace to the pipe ends outside. The piping has been that way for 8 years and I've never had this error code before.

As Seattle Pioneer said, this problem is definitely getting worse. The furnace now trips out in well under a day. The fact that the house cools down when the furnace trips out causes the furnace to run longer than normal after I reset the switch so that probably contributes to this problem.

Hey Boys, thanks for working on the weekends!

 

Put jumper on the bad switch and it should stay running to see if that's your problem and it sounds like it is since it follows the switch. It's a 24V circuit and doesn't matter about the wires. They'll go to either terminal so there is no danger of crossing anything. If it runs trouble free change the switch and enjoy your winter. There are limits as to how far you can run a vent pipe but where yours has been running trouble free for 8 yrs. I wouldn't bother with that plus the problem arises only when that same switch comes into play.

 

That's exactly what I did several hours ago. I figured since there's another rollout switch in the furnace and I don't see any sign of rollout it was a relatively low risk thing to try. I'll let you know tomorrow how that works out. It's warmer here today so the thermostat has not been calling for heat.

 

OK, so I bypassed the suspect rollout switch with a jumper wire yesterday. The furnace was running just fine this morning, but the switch had tripped out (I left it installed in the furnace in its normal location). I removed the jumper and bought and installed a new rollout switch. Just an hour later the new rollout switch had tripped out!

Any idea what is going on here? What do I check next?

 

It seems the rollout sensors (the old one and the new one) are telling me it's too hot in the combustion area of my furnace. Why it was too hot on the left side a few days ago and now it's too hot on the right I don't understand.

So what could cause the excess heat? What can I check? I should mention again this problem came on in a matter of a few days. So whatever it is developed pretty quickly. I've also stated I see no flame rollout when I observe the furnace through the view port. So what could be going on?

 

Have you changed the filter recently and are the room registers open? Lack of good air flow across the heat exchanger can cause roll out tripping.

 

Are both roll out switches the same temp. range. There should be a heat value on the disc, possibly 160 or so, just guessing on the temp. You can check for draft problems, chimney obstructions. Put your hand in front of the fire and see if you feel any heat coming back. You should be able to keep it there without feeling heat if you have proper draft. It sounds like a nuisance but did you try to switch the new one with the other one to see if you have the same problem.

 

The filter was recently cleaned (it's a reusable one). Interestingly, last week I closed two registers in an unused room. That's very close to when this problem started to happen. I've opened up two registers in another room. There seems to be plenty of air coming out the registers.

Both rollout sensors are identical 200 deg F open-on-rise units. The furnace air inlet pipe has a plastic grid filter that is clean and open. The flue pipe just opens to the air. I stuck a flexible hose in a few feet and felt no resistance. I really don't feel much heat when I hold my hand in front of the burner tubes. There is one original and one replacement flame rollout sensor in the furnace. Yesterday the one that failed was back on the left side (original sensor). The fail location has been moving back and forth between left and right.

I measured the gas pressure on the inlet and outlet sides of the gas valve. I have 10 inches water column on both. I took out the circulator fan. The vanes were quite clean. I checked the secondary heat exchanger and it was clean also; I did vacuum it. I also looked at the AC coil on top of the furnace and it was also clean. So I don't see anything in the furnace that could be limiting the air flow.

Any other suggestions?

 

It really doesn't sound like you have a problem other than the nuisance shut downs. Do you have a temp gage or probe and see what the temp is where the sensor is located. The sensor is there to protect you from carbon monoxide from a lack of draft. If that were the case though you would feel the heat especially where the disc is set at 200 deg. Where this disc I believe is mounted by the burner it shouldn't have anything to do with airflow from the plenum into the house since the plenum is sealed from the burners unless you have a crack in the heat exchanger but as you said, it follows the disc. It is very strange case.

 

I always seem to end up with these strange cases. It's never like I go to the basement and the furnace is laying on its side, and I say Aha!

I also thought of the temp probe to profile the temperature near the rollout switches but I don't have one.

How do I go about checking out the flue pipe to make sure it's not obstructed? Based on spott's comment it doesn't seem likely I could have a major restriction but at this point I'm about out of things to check.

 

Without seeing your setup is it possible to snake your exhaust line to check for obstructions. Electrical snake or equivalent or cut and check and the just repair with a coupling.
How about removing and relocating that disc away from the boiler temporarily which would be away from the heat and see if it still goes off. Just a thought. I'm beginning to think it has nothing to do with the boiler operation and possibly more to do with the circuit it's tied into. Just a thought.

 

I was also thinking about some way to snake something through the flue pipe. I do have an electrical snake. I was also thinking about taking a hollow plastic ball, tying a string to it, and using my shop vac to suck it though the pipe from the outside. I'm going to work on that tomorrow.

I took the door panel off the burner compartment yesterday morning. The furnace has been running fine since then, although it hasn't run a lot since it has been warm again. But that's much longer than it has previously run without a trip out.

Below, I hope, are pictures of the burner flames. Two pix of the left two burners, two pix of the right two. Does anyone see anything that looks like it could cause the rollout temp sensors to overheat?

 

I have a Goodman propane-fired furnace model GMS950904 CXA, about 9 years old. The flame rollout sensors (there are two) shut down the furnace in less than a day. Both click-to-reset sensors have caused the furnace to shut down. I replaced one sensor and it also causes fails. There is no flame rollout visible during start up or steady state run. If I remove the access panel from the combustion area the furnace will run for weeks without a problem. It seems the rollout sensors (the old ones and the new one) are telling me it's just too hot in the combustion area of my furnace.

I replaced the induced draft blower 2.5 years ago; the bearings are still quiet. The furnace air inlet pipe has a coarse plastic grid that is clean and open. I hooked up my big gasoline powered backpack leaf blower directly to the flue pipe and ran it full speed. Air moves freely and nothing like leaves or birds nests came out of the flue pipe. I measured the propane gas pressure on the inlet and outlet sides of the gas valve. I have 10 inches water column on both. I took out the circulator fan. The vanes were quite clean but I cleaned them anyway. I checked the secondary heat exchanger and it was clean also; I did vacuum it. I also looked at the AC coil on top of the furnace and it was clean. The furnace filter was recently cleaned (it’s a reusable type).

It seems like the air flow through the heat exchanger is not impeded nor is the air flow through the intake and flue pipes. What else can cause the furnace to run too hot? I’ve pretty much exhausted all the possibilities I can think of.

 

I merged your threads. If you start a new one.... all the same questions gets asked that were already answered.

Have you ever measured the temperature rise thru the furnace ?
Measure the return air just before it enters the furnace and measure the supply temperature when it leaves the furnace. The difference in the two is the rise. Acceptable rise is listed on the furnace ID plate.

 

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Ummm. In most cases the combination electric gas valve contains a regulator that steps the gas pressure down to a suitable level for the burner manifold.

Your results above suggest that the regulator isn't working or is set improperly, too high, which might easily overfire the furnace and cause flame rollout.

This issue is something to consider. You might need to find the pressure that should be set at the burner manifold. The gas valve should reduce the gas pressure to that level, which is commonly measured at the burner manifold through a 1/8" plug that can be removed to check the pressure.

 

If you have 10" manifold pressure on natural gas then your way overfired