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Strange, intermittent problem with furnace: flame detected, no call for heat

Strange, intermittent problem with furnace: flame detected, no call for heat

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  #1  
Old 02-28-20, 07:33 PM
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Strange, intermittent problem with furnace: flame detected, no call for heat

First post but been lurking for awhile. Some relevant info as requested in the sticky:

Natural Gas furnace, Amana 80SSE, 21+ years old. ( GUIC070DA40 )
Control Board is a White-Rodgers 50A50-288, assuming this is original
Thermostat is an Ecobee 3, likely irrelevant info for this.

When the furnace runs, it works great. It'll get up to temp without any problems. However, a few seconds after the thermostat cuts it off and the gas valve closes, the board will flash continuously indicating a flame was sensed with no call for heat. Then it locks out heat for an hour, but I can get the AC to run with no problem. It is an intermittent issue- it may take 2-4 cycles to get the board to flash. I can get it working again by simply cutting power to the furnace & turning it back on again.

So far I've cleaned the flame sensor, but it didn't help. Checked the flame sensor micro-amps, no problems there. Flames are nice & blue, no strange noises or rollouts, etc. What else could this be and what else should I check?

Thanks in advance.
 
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Old 02-29-20, 02:58 AM
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I rarely worked on any small heating unit, just large commercial units, but when we encountered this same or a similar problem, the problem was almost always a bad control board or for us a bad "primary control".
 
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Old 02-29-20, 04:21 AM
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Hi, check to be sure you have a good ground connection, this link maybe helpful.

https://climate.emerson.com/document...us-4290120.pdf
Geo
 
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Old 02-29-20, 12:17 PM
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A ground path from the burner to the control board is critical for proper operation. A bad ground between the burner and the board can cause a lack of flame sense but not what you are getting. A bad ground between the furnace and the board can cause your problem.

Your board gets its ground from the large 12 pin molex connector.
Try removing and reseating it several times.

If not that..... board replacement may be your next step.
 
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Old 03-02-20, 08:24 AM
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Appreciate the fast responses. I checked the ground and it was clean & tight. Seated & unseated the 12 pin connector a few times, everything was clean & tight there too. Unfortunately the same error code came up. I thought maybe the gas valve was closing slow, so I checked voltage but when power is cut the flames shut off immediately. Then it takes 3 seconds and the board starts flashing. So likely a bad board. Fortunately I have a twin 2nd unit (same age) that runs perfectly, so I might experiment & swap the board.

However it is starting to get warmer (Texas coast) and I don't think I'll need the furnace the rest of the year. This same system is not cooling so great, found out refrigerant is 20 psi low and the evap coil is leaking. Going to charge it up & see what happens over the summer but I'm looking at replacing the whole system now.

Thanks again.
 
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