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I wonder if there was a OEM issues or a recall on the boards myself I tried to call the manufacturer but they don't like to return calls

Wonder if they are using a non OEM replacement board? Like the issues that were had when using ICM boards to replace Carrier OEM boards?

I don't know how much a manual is going to help here. Afterall; the unit is cold, the limit is closed (and was jumped), and the board still throws a limit error. All points towards board...which was replaced. But with the right board?

Originally Posted by stuff350

Waiting iom manual, to come in ill let you guys know what's wrong with it when I find out. Just also found out students have been trying to trouble shoot this unit for a year now to try to figure out what's wrong with it

Reminds me of an experience in Aircraft maintenance school in the 1970's... Without knowing what we were doing... a few of us decided to 'fix' the bucket of bolts rotorcraft in the back lot... Did not know we had taken on one of the more complicated (and fewest parts available) rotorcraft ever built...

You guys have attacked what used to be the most advanced design of a residential furnace... Problem is... without some 'manuals'... it is literally fishing in the dark without worms.

Please do let us know what you find and learn... always glad to cheer on someone learning.

BTW: You might want to apply for PRO status based on you being a student... the LARGE majority of cool stuff at H-talk is behind the PRO door... you will be amazed. There is a section called the educational forums... would keep you glued to your computer for weeks...

Waiting iom manual, to come in ill let you guys know what's wrong with it when I find out. Just also found out students have been trying to trouble shoot this unit for a year now to try to figure out what's wrong with it

Originally Posted by Joehvac25

It's a school project and they don't have a manual?

Sounds like a couple of other schools I attended decades back...

Originally Posted by stuff350

I like that point you made with the parts changing hack, there isn't much of a manual that came with the unit and yes I did clear the board even changed the board.

It's a school project and they don't have a manual?

Originally Posted by stuff350

I checked with a volt meter

Seems to me you've caught the extremely rare impossibility.

Please let us know the resolution. And be very cautious when jumping around safeties. Especially if anyone you care for is living upstairs.

I checked with a volt meter

It's cold. It flashes an open limit before it fires. You've replaced the board and still get an open limt error before ignition. And you could not find any open safeties?

How exactly did you confirm the limit was closed?

The WHY's are the key to being successful (technically) in this business.

I suspect if you approached the faculty at your school... they could find you a current IOM (installation and operations manual) manual for that furnace. Give them the model and serial... and see if they can get it for you.

I like that point you made with the parts changing hack, there isn't much of a manual that came with the unit and yes I did clear the board even changed the board.

Might clear the board... then start over... sometimes codes get 'stuck' in a board... power off and count to 10... then power back on.

If you are in school and doing a project... I would go through the entire troubleshooting chart in the IOM manual (I assume they gave you the manual)... sooner or later you will find something of interest.

Then when you KNOW what was related and what was not... you can explain the WHY's of what was wrong and how to fix it.

Knowing the WHY's is the key to this industry... otherwise... one becomes a parts changing hack.

The burner don't fire off at all right away it gives off that high limit error

Check for three things:
Faulty limit control
Insufficient combustion air
Unstable flame pattern


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What I do is work with the tech manual right in front if me? There are too many mistakes that can be made with electrical troubleshooting and you need to follow protocol while troubleshooting and don't use jumpers in the wrong places, good luck.

Sorry, I was not specific when I said jumped it at the board, I'm an OSU -it student in the HVAC program and am working on this project for extra credit. I jumped it from the back side of the plug before it goes into the board .

Originally Posted by TriWorksInc

Thats what I was getting at, just from the post theres a possible drowning situation there.

Yeah... If this guy is trying to DIY this furnace problem... he may spend a LOT more $$$ on his learning curve than calling a Rheem person and paying them to do the work properly... not to mention all the time, aggravation, and possibly nights on the couch 'cause mama is cold and irritated...

Originally Posted by ga-hvac-tech

Hmmm... RGFD... that is a MOD furnace (modulating). You really need to get a RHEEM guy out there... this furnace is unique... not an average unit and not easy to service unless one understands the unit.

Furnaces are not DIY products... folks can cause a lot of damage and potentially create an unsafe condition if they try.

Thats what I was getting at, just from the post theres a possible drowning situation there.

Originally Posted by stuff350

I have a rheem 90 plus series model number rgfd07emcks over temp limit error 33, right when the unit starts up cold it flashes code 33 over temp limit. I have used the volt meter took it all the way to the board. I could not find an open anywhere. I then jumpered the whole circuit at the board still got the same code. I figured it was a bad logic board so I changed out the board however still have the same error code. '
Does anyone have any ideas

Jumping things out on that board can screw the board up.


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Hmmm... RGFD... that is a MOD furnace (modulating). You really need to get a RHEEM guy out there... this furnace is unique... not an average unit and not easy to service unless one understands the unit.

Furnaces are not DIY products... folks can cause a lot of damage and potentially create an unsafe condition if they try.