Honeywell S8910U "Internal Failure" multiple boards

4 years ago

I've got an amana aircommand 80 furnace that stopped working last week. It had a white-rodgers control panel that had a steady-red light and the manual indicated that this meant that the panel had to be replaced. It was replaced last year. I decided that maybe that brand just keeps failing and heard the HoneywellS8910U was a good replacement so I ordered one and installed it, but the replacement is now giving Honeywells version of the same issue - four flashing lights that the manual says is an "internal error". Even tried another S8910U and yep, same issue. Unless I happened to get two defective control boards this week, what else could possibly cause a furnace to throw logic board errors? I tested that AC voltage coming into the board and it looks within spec. What else can I check?

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4 years ago

To Elmer Fudd: Very helpful! Just shut up...😏

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Comments (7)

mike_home
4 years ago
Are you getting 3 or 4 light flashes? The S8910U installation manual says 3 flashes indicate a internal error. I see no mention of 4 flashes.

What was the model number of the White Rogers module? Did you set up the Honeywell unit as specified in the installation manual for the White Rogers module you replaced?
Marc Hanish thanked mike_home
Marc Hanish
Original Author
4 years ago
The manual that came with it says 4 flashes (see pictures) It was a white Rodgers 50e47-170. I did set all the dip switches and wired it using the instructions in the manual specific to going from the white Rodgers model.
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mike_home
4 years ago
last modified: 4 years ago
I searched for the Honeywell S8910U installation manual and see it is different than the Resideo S8910U3000. It appears Resideo has made changes to the module.

It is possible, but highly doubtful you purchased two bad modules. I saw the following in the manual:

Four yellow flashes indicate an internal error. The most probable cause is an S8910U logic failure. Start a new call for heat and if the four-flash signal returns wait 1 to 2 hours and repeat the last step. If the four-flash signal returns again, replace the S8910U.

Did you try waiting 1 to 2 hours and repeating the last step? If that doesn't work have you tried disconnecting an output and seeing if it shows a different indicator?
Marc Hanish
Original Author
4 years ago
Yes I tried waiting and repeating and same issue. I tried disconnecting each wire one by one and has the same problem for all wires except when I disconnect the 24v line the control board doesn’t light at all (I’m assuming that is how it gets it’s power).

Used the multimeter and am getting about 26v on that 24v line. Seems like not too far out of range but could that be the problem? Looks like it comes from the thermostat so maybe a faulty thermostat? Just guessing here
Elmer J Fudd
4 years ago
"Just guessing here"

That's clear. Please be safe and call a knowledgeable HVAC person to fix the problem.
Marc Hanish
Original Author
4 years ago
I would but there is a six month wait for a repairman in my area :)