Rheem Classic 90 Furnace - Won't Stay Lit - HELP

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Old 11-11-12, 02:18 PM
hvactechfw's Avatar
Join Date: Jan 2011
Posts: 6,245

Not a good ideal to clean the sensor w/ stell wool.. It's too harsh... dollar bill does the trick. I'd plan on replacing the sensor down the road.
WHAT?! I use steel brushes and or brass brushes..... Steel wool is fine! Flame sensor should never have to be replaced unless there is too much of an oxide on the flame sensor to get it clean or if it (the metal part) turns inside the ceramic (white part).
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Old 11-11-12, 02:40 PM
Jay11J's Avatar
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 18,427
From what i was taught in school, if you sandpaper or anything aggressive, it will score/grooves the sensor and removes protective coating on the sensor, and sand papers can leave enough silica so the flame melts it into glass.
Old 11-11-12, 02:52 PM
hvactechfw's Avatar
Join Date: Jan 2011
Posts: 6,245
I agree about NOT using sand paper as I have found that any sand left on the sensor does turn to glass and acts as an insulator to the flame. However, steel wool is perfectly fine. Now, I always use 00 or 000 steel wool, but that is just my preference. I dont know of any protective coating on a flame sensor. Any type of coating could act as an insulator to the flame.
Old 12-06-14, 06:05 AM
Join Date: Dec 2014
Location: USA
Posts: 1
Rheam 90 classic +

My furnace is doing the same thing, ignites burns for 8 seconds and shuts off.
Cleaned all the lines and replace the flame sensor NO GO.
Control board has 2 green led's lit .
I need help.
Thanks in advance
Old 01-16-15, 08:02 AM
Join Date: Jan 2015
Location: United States
Posts: 1
Fixed the Problem by Cleaning the Flame Sensor

I have a Rheem Classic 80 furnace that would ignite but not stay lit. Cleaned the ignition sensor which was easy to get to and the flame sensor which was under the burner plate and it fired up and stayed lit. The flame sensor was about 6" under the burner plate. Easy to get out, but tough to get back in. Used the old piece of paper shim trick to get the screw to "stick" in the socket and it was much easier to position the screw and get it back where it belonged.

Last edited by Shadeladie; 01-16-15 at 08:21 AM. Reason: Link removed
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