Rheem furnace: overheating error


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Old 02-09-16, 02:37 PM
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Rheem furnace: overheating error

Good Day,

Good afternoon,
I am having some overheating trouble with my HVAC and I hope someone who has solved this issue before could help me.
First, some background:
- I live in Alexandria, VA – hot summers and cold winters.
- The house is a 1700 Square Foot Split level. The HVAC is in the basement and the return is in the top floor ceiling.
- This is a Rheem Heater with Electric Ignition – no model number on the outside cover, but the inside sticker shows MODEL: TUE100A936K0 ; SERIAL NUMBER: M175KH62G
- Natural Gas heater
- Nest 3rd generation thermostat

EARLIER PROBLEM (resolved, but just so you know the background)
Moved into the home December 15th, 2015, so have only been in the house a month and a half. On the day of our blizzard in mid-January the HVAC kept restarting the ignition sequence after 8 seconds, so I cleaned off the flame sensor and bought a new one as a backup and it worked fine.

CURRENT PROBLEM:
Yesterday (3 weeks later, while running the heat all day, I noticed the house was getting cold and realized the vents were blowing cool air. I went downstairs and restarted the HVAC. I sat there and watched the flame, thinking it would be the same problem with the ignition sequence restarting over and over like last time, but this time it stayed on. I replaced the flame sensor with the new one just in case, put the HVAC cover panels on, and left the heat on and sat there waiting for something to go wrong. About an hour later, the same cold air blowing in the vents.

Went down again and restarted the thing, this time I stayed and watched it for a long time, maybe half an hour, then I noticed the flame cut off but the fan was still blowing. I looked at the LED indicator and saw the blinking code for:

THERMAL PROTECTION DEVICE OPEN
So, the HVAC is overheating. After troubleshooting, I realized that this only happens when both of the panel covers are on. If I leave the top cover off (the one that covers the flames), I don’t have a problem. I read about the issue of overheating and read about dirty filters causing the problem. I put in a new filter and I have the same problem now.

What could be causing overheating when the panel is on?

I disassembled the gas jets and cleaned them, dusted everything. Made sure all the vents in the house are wide open so they could blow out the hot air.

Is there anything else I can do before I call a repairman?

TT
 
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Old 02-09-16, 02:56 PM
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Did you also check the return grille and ductwork to see if there are any obstructions?
 
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Old 02-09-16, 05:02 PM
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> \



I would call that an unrelated coincidence.

You done a good job of diagnosing the problem as a furnace that is overheating.


Usually, this is because of something that is impairing the air flow through the furnace. If not enough air goes past the heat exchange, the furnace can't get rid of all the heat produced and it will gradually overheat.

So check all parts of the air flow system ---- be sure the return air grill(s) are unobstructed. Be sure the fan motor is coming up to speed. Check to be sure that the fan blades are not choked with dust and dirt.

Since you probably have AC, you probably have an AC coil in the furnace, which can get plugged up with dust and dirt --- so use a flashlight and mirror as need to carefully inspect that coil to see if it's plugged up.

Sometimes sound insulation in the duct work can get pulled loose and plug things up. Finally, check to be sure that most of the warm air vents are open.
 
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Old 02-09-16, 05:36 PM
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The grille is in the upstairs hallway ceiling and is routed through the attic, down past the upstairs bathroom wall, and down into the basement furnace.

The grill is large, about 3 or 4 feet long by 1 or 2 feet wide, I see no obstructions. I glanced into the return by the return duct by the unit (through the air filter slit) and saw nothing wrong.

Also as an update - the new flame sensor is also having trouble igniting (with or without the panel cover on). Do new flame sensors need to be rubbed with steel wool first, or is there a general breaking-in period?
 
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Old 02-09-16, 05:39 PM
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Welcome to the forums.

The flame sensor rod does nothing. It's an inert piece of metal that sits in the flame. It may glow red from the heat of the flame but it in itself does not.

If you had a flame sensor problem..... the burner would shut off within six seconds of the burner lighting.

You said intermittent ignition.... I believe you have a hot surface igniter.
 
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Old 02-09-16, 05:42 PM
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Thank you for your reply - all of the warm air vents are open, but I did not clean as thoroughly as you mentioned.

This is a nice old house constructed in the 1950's, but a lot of it was not properly maintained - attic insulation in bad shape, etc.

So far, I have only removed the panel cover, the jets, the gas tube leading to the jets, and the gas regulator and cleaned cleaned out all of the dust in and out of those areas with gas duster and electrical contact cleaner for the wire contacts.

This weekend I will take out the draft inducer (correct?) and open the entire unit for a thorough cleaning - in the fan and coils as you said - and post if that made a difference.
 

Last edited by ttrifko2; 02-09-16 at 06:52 PM.
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Old 02-09-16, 05:57 PM
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Sorry, to clarify - there's two issues: one is that the flame will cut out after heating for an extended period of time, and with the diagnostic code suggests overheating.

Then - if the heater is starting up as part of a normal heating/cooling cycle, it will go through those start-up hiccups, which suggests a flame sensor issue on top of the overheating issue. This is a brand new flame sensor straight from the package.

Is there a way to test it with a multimeter?

Yes, I have the electric igniter.
 
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Old 02-09-16, 06:00 PM
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If you're confident the return air is not obstructed somehow, an earlier post suggested checking the fan to make sure it is not dirty. The fan in question is a squirrel cage blower- the vanes can get coated with dust and (in my case) pet hair. Mine was so clogged the vanes became the wrong shape, so it couldn't move air as intended. To check if it's dirty reach in and run a fingernail along a vane: if you bring out a bunch of crud, remove the blower for a deep cleaning.

The reason it works with a panel removed is because the open panel allows air in from a different source, and the system doesn't have to work as hard.

PS- I'm around the beltway from you, at 9:00 compared to your 6
 
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Old 02-09-16, 06:02 PM
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No need to touch the draft inducer. Actually.... you can remove the rubber hose from it and clean out the tiny hole thru the fitting into the blower. It will be very small.... a large paper clip or very small drill bit can be used. It needs to go into the blower at least an inch or so.

If you want to be thorough.... open the blower door and remove the blower and housing from the furnace. Check and make sure the blower wheel is clean. Once the blower is out you should be able to look in/up and see the A/C coil.

I haven't found the service manual yet to see the furnace setup.
 
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Old 02-09-16, 06:51 PM
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Word up to my homies in MD! Rented a $400 a month apartment in Montgomery Village once...

I will take out the blower from its housing and hose it down tomorrow and post a picture.
 
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Old 02-09-16, 06:57 PM
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Ok... I didn't realize you still had the flame shutting off in 8 seconds. I thought it was just an over heating problem now.

The flame rod creates a path from the actual flame to ground. That means the flame rod must be fully in the flame. Sometimes the mounting brackets are off a little. You can check the performance of the flame rod by using a meter with a microamp (ua) scale on it. Let me know if yours has that scale.
 
 

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