roll-out tripping!

Hi guys,

new guy on here, working on a HEIL Model # H9MPD075F12A2 that is tripping the rollout swith after watching the thing run and start many times it has become evident that there is no flame rollout it is simply overheating and it is only the right switch which mounts a little higher on the box than the left side, I have switch the switches around and it trip on the same spot. the furnace does have a little higher than normal heat rise but nothing to alarming maybe 50-60 but it is already on med-hi speed. filter clean and all registers open. pressure on the collector box is 2.80" H2O unfortunatelly cant get a reliable reading @ the burner box as its cabinet not just the box. Both intake and exhaust returned my golf ball, so not sure if I want to condem the secondary HE or is something else going on. I wish there was some data on the design static of the draft @ the collector box oddly enought I think it is related to the high heat rise but how?::DD:

Could be over-fired. Did you check gas pressures?

I used to install Heil equip. but it's been a few years since I sold any. Is this a 90+ or above furnace? Sounds like it is. Sounds like you have a leak in the burner box somewhere close the the roll out switch that's tripping. You must have a blockage of some sort in the air flow causing the high heat rise and tripping the ROS

I worked on my first goodman furnace for a friend a few months ago doing the same thing, it was a 90+. I never saw any flame rollout but it tripped when it was cold and had to run a lot overnight.

I went down on the gas pressure to about 3" and it helped a lot but didn't fix. after cleaning the secondary and didn't get better results we changed out the heat exchanger and took care of the issue. I couldn't find a hair crack in it but I guess it had to be there though.

Easy to diagnose with a combustion analyzer...

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Originally Posted by chippert

I worked on my first goodman furnace for a friend a few months ago doing the same thing, it was a 90+. I never saw any flame rollout but it tripped when it was cold and had to run a lot overnight.

I went down on the gas pressure to about 3" and it helped a lot but didn't fix. after cleaning the secondary and didn't get better results we changed out the heat exchanger and took care of the issue. I couldn't find a hair crack in it but I guess it had to be there though.

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I would bet if you took the plate off the hot side of the secondary, you would have found a lot of rust flakes plugging some of the tubes going through the secondary.

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Originally Posted by chuckcrj

I would bet if you took the plate off the hot side of the secondary, you would have found a lot of rust flakes plugging some of the tubes going through the secondary.

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There was a little junk in them. I used a 45 caliber bore to clean them. looked like need when I got done though.

I thought about that but could not make any sense why it would start all of the sudden, but that will be next probably monday!

sorry, forgot to mention that has been done the flue readings where about 89% efficiency 122F & 6.2 CO

I don't know what you mean by hot side of the secondary?? but I've inspected the collector box, I guess they are prown to cracking and while it was off all the pipes of the secondary looked pretty clean, some rust but nothing flaking off.

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Originally Posted by frustraded tech

sorry, forgot to mention that has been done the flue readings where about 89% efficiency 122F & 6.2 CO

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Need CO and O2 readings over time. Have to watch those readings over the whole run cycle. Just one set of readings taken at one point in time is almost worthless.

I don't have my notes and i forgot what the O2 was but it ran almost 45 min it started with a 92% efficiency later on dropped to the 89%, i almost thought i had it figured out because it ran so long. one important fact since i was there the first time over a week ago the unit has not tripped by a trial and error a combination of leaving the upper door on and the intake pipe off, then the unit appear to not trip, but I am having a hard time making sense of why does it help to leave the door on??? again with the door off and the pipe on it trips. :gah:

Did you check the back of the inducer motor, to make sure the restricter plate hasn't come apart or crumbled? Ive had many of headaches over those dumb things.