Rollout switch trips

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Chevsky

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Nearing desperation with a furnace that's tripping flame rollout sensor. ICS/ComfortMaker RPJ-II LP gas furnace.

Well, it's working now, but that's only after I tore down the furnace to inspect the heat-exchanger for cracks, removed and cleaned the blower cage fan, and disassembled and reassembled the burner, gas manifold and igniters, and inspected the chimney and exhaust flues. Why it's now working is a mystery... (I think this furnace has it out for me)

Worth noting is that I have two LP gas furnaces (w/AC) and an LP hot water tank all on the same single-flue chimney. Primary 100K-btu LP furnace + H2O in the basement, and a smaller 75K-btu LP furnace on the second story.

It took me a couple weeks to finally realize the flame rollout had tripped. [Credit to "Word of Advice TV" and Greyfurnaceman.com YouTube channels: 10 reasons your rollout switch is tripping] I got it light but the flame rollout sensor/switch trips every 1-3 hours. I replaced the switch (seemed iffy -- have to push on it hard before a very faint reset click) but the new one keeps tripping too. (kept tripping -- 24 hours later and it's still working ok. I may have inadvertently fixed the furnace, or turning down the upstairs heat has stopped the problem reaction, or perhaps it's just taking a short vacation from mocking me)

Symptom is that the furnace is blowing cold and the burner isn't lit; I'd feel a cold breeze in the house; Go down to the basement, power off the furnace, reset the rollout switch, power-on the furnace, which would then ignite just fine and heat for a while; Eventually I'd get tired of watching the furnace waiting for some clue... I'd return to my sofa; Then 1-3 hours later it's blowing cold again. Rinse and repeat.

So I assume at some point the flame is indeed rolling out. (I've only actually witnessed it when I've reset the rollout switch without first powering off the furnace. In that case it happened because the furnace ignited just as the induction fan stopped)

Can anyone suggest things to check if this behavior starts up again?

Perhaps it is a bad heat exchanger, but maybe it's a chance startup (or just running) of the 2nd story furnace at the same time the basement furnace tries to startup. Or maybe it's while the basement furnace is running, AND the H2O is running, AND then the 2nd story furnace starts up and causes enough back-pressure to cause a rollout. One strange (seeming to me, but what do I know) behavior is that while watching the basement unit: it runs (heating) for some good long while, but then stops short of reaching the set temp... the burner stops; then a minute or two later the induction fans stops; then in a few minutes the blower stops -- BUT at that moment the induction fans starts, then the burner, and then the blower. This seems to cycle 2-3 times -- a heating cycle stopping and going immediately back into a heating cycle. Eventually it stops completely when the target temp is reached.

I tried my LP supplier for service, but over-the-phone response: "Your heat exchanger is cracked, blower is pushing air into the combustion chamber and blowing the flame to roll out. Furnace is junk. I can replace for $5K". Two years ago it was the Honeywell Smart-valve. $500 to replace. Last year the same symptom... but this time I took to it myself, and traced it down to a clogged pilot orifice -- a $3 part. Hmmm.

Yup it's an old unit, but I just want to buy some time to spec out a whole-system upgrade rather than throw money at this one furnace. I've posted another thread (here on my first day :D) asking for thoughts on a two-system hybrid LP(s) + multimode heat pump(s) vs combining these two into a single zoned setup with some duct rework. Someday it will be like that scene in Office Space, out in a field with the printer...

Thanks all (long post, I know)
 

Fitter30

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First look at the burner burning with blower off take note of each burner and the tip of the flames. Then with the burner and blower both running has the flame changed. Is any of flame pushing out towards the front of the burner that would be a problem with a crack in the heat exchanger. Other problem is when the burner doesn't light correctly and it starts burning back in the orfice. Did your pull all the burners when checking the heat exchanger and look with a mirror and flashlite in each section.
 

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@fitter30 -- No, there's no change in the any of the four burner flames when the blower comes on.

I've finally witnessed the issue. The furnace begins to shutdown -- the burner stops, then in 1-2 minutes the draft fan stops, then in a minute or so the problem happens. You'd expect the blower to stop, but instead the burner starts up without the draft fan running. As you'd expect without the draft blower running, the flames all struggle to stay contained and fill up the burner space, and finally one of the the rollout switches trip. Then the furnace enters the state of having the duct blower run indefinitely, typical to when a rollout switch trips. When this "restart-without-draft-fan" event happens, the draft fan is still coasting to a stop when the burner lights, but is obviously not receiving power. To rectify, I kill the power to furnace, reset the rollout switch, and turn the power back on.

Now this doesn't happen reliably. Rather, the furnace can operate fine for a day or a few hours, which is what was making it elude me (I'd get tired of sitting by the furnace waiting for something out of the ordinary happen). 2 weeks ago I disassembled most of the furnace -- removed the gas valve and manifolds, burners, blowers, and inspected the heat exchanger. All looked fine, and after I reassembled it, the furnace worked fine for about 10 days. Prior to that I also swapped the main controller board between my two furnaces (my other is the same make/model/year and uses the same board), and the problem stays with this furnace.

What would cause the furnace to shutdown, and then startup again without the draft fan running? (it's a new draft fan, installed in October at the beginning of the season -- the old one had seized up). Could it be the overheat switch? I replaced the filter in October, and we don't have particularly dusty habits; the old filter looked not-too-dirty. I believe that furnace frequently cycles off and then immediately on again, mostly without the rollout occurring, when the thermostat is still calling for heat. This seems odd to me.
 

Chevsky

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The model number is GNE100J20A1 -- ICP/International Comfort Products, with a label "ComfortMaker RPJ-II" on the cover.
I took out the filter, and now it's stopped rolling out. I waited to reply back until I was sure, and it's been 36 hours and no roll out.
I guess the filter was restricting flow and causing short cycling. My guess is that the high temp switch is opening, the burner goes off and a short time after the draft inducer fan, and then before the blower stops the high-temp switch closes; since the thermostat is still calling for heat the burner starts up again. But somehow the logic in the board doesn't start the draft inducer. Is this typical -- after the trip circuit opens and re-closes, the control board allows burner startup from non-initial off state? Hmmm...
I'll reinstall the filter, connect up a meter to the high-temp switch, and sit-n-wait for the roll out to be sure it's the trip circuit opening and the high-temp switch doing it.
If this is what really happening then I may have duct-work problems (besides the controller behavior). The filter I'm using is FPR12 and by its appearance looks much more restrictive than a cheaper filter (DP complained about smells from the ducts so I got this one). So it's back to cheaper filters for me.
The home is mainly a single story, so all ducts are on the basement ceiling and accessible. The ducts are a combo of fiberboard and flexible. The flex is held up by straps, and some of them sag. Seems to me that this causes some restriction. Perhaps over the years this has been getting worse, and my choosing an FPR12 was the tipping point.
So today I'll pickup some lighter filters and straighten out some ducts to see if I can get it stable again.
If anyone has further suggestions then please share.
 
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Chevsky

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I switched back to lightweight filters and the short cycling stopped. FPR 4 (HD, dunno what the MERV rating is) - these are 1" thick (25" x 16"). The slot is cut from the fiberboard that's glued to the side of the furnace with mastic. Perhaps I'll see if I can widen the slot to take thicker filters.
 

subbu

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Hi @Chevsky , I hope you are well, I just came across this thread and I am facing the same issue with my furnace. My switch keeps tripping if the heater is running for more than 12 minutes. So I set the heat to 19.5C so that the burners are not on for more than 10 minutes and it is running fine. Please advise how did you fix your problem or any insights on to what's going on with my furnace ?
 

Fitter30

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Hi @Chevsky , I hope you are well, I just came across this thread and I am facing the same issue with my furnace. My switch keeps tripping if the heater is running for more than 12 minutes. So I set the heat to 19.5C so that the burners are not on for more than 10 minutes and it is running fine. Please advise how did you fix your problem or any insights on to what's going on with my furnace ?
Look at the flame with and without the blower. If the flame is lazy with no blower burners could be dirty, but with blower on if flame pushes down and or out bad heat exchanger. Repair is a new exchanger or furnace.
 
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