Luxaire PCUHBLD12N100A gas won't stay on
#1
11-13-22, 02:54 PM
Luxaire PCUHBLD12N100A gas won't stay on
I'll start by saying that the flame sensor was replaced and both the new and the old sensors read 1-2 microAmps.
Furnace goes through proper start up sequence. On cold start, flames stay lit for 60-70 seconds, then gas shuts off. Will recycle 4 times, each time gas will stay on for 10-25 seconds, then lockout. Red LED flashes 8 times (code: loss of flame). If I reset power from the breaker and then retry, the first gas cycle only lasts 30-40 seconds, as if being warm shortens the time to fail. Furnace did run properly in mid-October during a 3 day cold snap.
Furnace goes through proper start up sequence. On cold start, flames stay lit for 60-70 seconds, then gas shuts off. Will recycle 4 times, each time gas will stay on for 10-25 seconds, then lockout. Red LED flashes 8 times (code: loss of flame). If I reset power from the breaker and then retry, the first gas cycle only lasts 30-40 seconds, as if being warm shortens the time to fail. Furnace did run properly in mid-October during a 3 day cold snap.
#2
11-13-22, 03:55 PM
Group Moderator
Welcome to the forums.
1-2 ua is not excessively high. It's considered low on many furnaces.
The Luxaire boards usually have the flame rod current printed on them.
Is the flame rod completely engulfed in the flame ?
You need to identify the problem before it goes into lockout.
When it fails.... it should flash a code and then recycle.
1-2 ua is not excessively high. It's considered low on many furnaces.
The Luxaire boards usually have the flame rod current printed on them.
Is the flame rod completely engulfed in the flame ?
You need to identify the problem before it goes into lockout.
When it fails.... it should flash a code and then recycle.
#3
11-13-22, 10:44 PM
Hi and thanks for the response.
Both the new sensor and the old are giving the same value on the multimeter (oscillating between 1 and 2 uA - meter doesn't do decimals), so I assumed they were both okay. It's a White-Rodgers 50A50-241 board (York 031-01266-000 - image here: https://i.ebayimg.com/images/g/OZQAA...75/s-l1600.jpg ) and I didn't see anything on it about the sensor current. The sensor is completely engulfed, yes. The fact that the gas stays on past the 10 second "no flame" safety cutoff makes me think it's not the sensor.
If I disconnect the sensor completely, the gas does shut off after 5 seconds, waits 1 min (ventor blower stays on), then tries again. After 3 tries, the blower motor comes on and I get the 7 red flashes code (no ignition) instead of the 8 flashes (loss of flame).
Should I try another sensor or go ahead and replace the board? Is there another test I could do?
Thanks again.
Both the new sensor and the old are giving the same value on the multimeter (oscillating between 1 and 2 uA - meter doesn't do decimals), so I assumed they were both okay. It's a White-Rodgers 50A50-241 board (York 031-01266-000 - image here: https://i.ebayimg.com/images/g/OZQAA...75/s-l1600.jpg ) and I didn't see anything on it about the sensor current. The sensor is completely engulfed, yes. The fact that the gas stays on past the 10 second "no flame" safety cutoff makes me think it's not the sensor.
If I disconnect the sensor completely, the gas does shut off after 5 seconds, waits 1 min (ventor blower stays on), then tries again. After 3 tries, the blower motor comes on and I get the 7 red flashes code (no ignition) instead of the 8 flashes (loss of flame).
Should I try another sensor or go ahead and replace the board? Is there another test I could do?
Thanks again.
#4
11-14-22, 02:30 AM
Additional info.
I timed the cycles with my phone's stopwatch:
1st gas burn: 47 secs
Off for 17 secs (igniter glows)
2nd gas burn: 16 seconds
Off for 17 secs
3rd gas burn: 23 seconds
Off for 17 secs
4th gas burn: 15 secs
Off for 17 secs
5th (and final) gas burn: 24 secs
Lockout
Everything else appears to be functioning normally. The venter motor comes on first and the gas doesn't fire until 20 seconds later. The blower motor kicks on 30 seconds after the gas ignites. Then the gas cycling on/off begins at around 1 minute 7 seconds after system start.
Eventually the lockout with the 8 flash led error code of "loss of flame".
Not sure if this is helpful info or not. The times above were from a warm start. If I start from cold after the furnace has been off for some time, the first gas on cycle seems to last longer, perhaps up to 80 seconds.
I timed the cycles with my phone's stopwatch:
1st gas burn: 47 secs
Off for 17 secs (igniter glows)
2nd gas burn: 16 seconds
Off for 17 secs
3rd gas burn: 23 seconds
Off for 17 secs
4th gas burn: 15 secs
Off for 17 secs
5th (and final) gas burn: 24 secs
Lockout
Everything else appears to be functioning normally. The venter motor comes on first and the gas doesn't fire until 20 seconds later. The blower motor kicks on 30 seconds after the gas ignites. Then the gas cycling on/off begins at around 1 minute 7 seconds after system start.
Eventually the lockout with the 8 flash led error code of "loss of flame".
Not sure if this is helpful info or not. The times above were from a warm start. If I start from cold after the furnace has been off for some time, the first gas on cycle seems to last longer, perhaps up to 80 seconds.
#5
11-14-22, 09:14 AM
Another update.
The fine people at Johnson Controls (Luxaire) responded to me with the PDF manual which shows the normal flame sensor current for my control board is 2.0 μA. Low flame signal control lockout is 0.15 μA. My reading is between 1 and 2 μA (the multimeter oscillates between the two values).
The fine people at Johnson Controls (Luxaire) responded to me with the PDF manual which shows the normal flame sensor current for my control board is 2.0 μA. Low flame signal control lockout is 0.15 μA. My reading is between 1 and 2 μA (the multimeter oscillates between the two values).
#6
11-17-22, 08:29 PM
I replaced the control board and the problem continues. The board is sending 24v to the gas valve, but it's shutting off for an unknown reason. When it shuts off, the flame goes out and then I can hear the valve click open and rapidly close again. I think the flame sensor is shutting it on this quick retry. Then the 17 second pause and it goes through the whole cycle four more times. Then lockout.
I can't have a 2nd board with the exact same issue, can I? Or is there something wrong with the gas valve/solenoids? What could be causing the control board to stop sending 24v to the valve?
Please help, it's really getting cold outside.
I can't have a 2nd board with the exact same issue, can I? Or is there something wrong with the gas valve/solenoids? What could be causing the control board to stop sending 24v to the valve?
Please help, it's really getting cold outside.
