GMP075-3 abnormal startup


  #1  
Old 11-29-17, 08:57 AM
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Post GMP075-3 abnormal startup

I have not previously seen this abnormal sequence - I can't figure out why it doesn't do the normal 30 second draft blower before igniter before gas valve sequence - any advice?

This is what it is doing:
  1. Thermostat sends heat signal
  2. Draft blower starts
  3. 10 seconds later the gas valve opens releasing raw gas up the flue
  4. four or five seconds later the hot surface igniter starts to glow
  5. two or three seconds later the gas valve and the igniter shut down before the igniter gets hot enough to ignite the flame
  6. seven or eight seconds later the draft blower shuts down
  7. A few seconds later the draft blower starts back up before it has time to spin all the way to stop, and then the furnace starts and completely cycles with a normal sequence.
Ralph
 
  #2  
Old 11-29-17, 10:44 AM
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That is odd, the ignitor should start first then the gas valve opens. What code are you getting ?

I see now that board doesn't have LEDS. Check the ignitor for any cracks.
 

Last edited by skaggsje; 11-29-17 at 11:31 AM. Reason: Added
  #3  
Old 11-29-17, 11:21 AM
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No codes - the red LED on the board stays solid. Yes, I also think it odd that the gas valve opens before the igniter is energized. And, then it works fine the second time it tries.
 
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Old 11-29-17, 11:43 AM
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Time for a new control board.
 
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Old 11-29-17, 04:25 PM
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I agree that you need a new board
 
  #6  
Old 11-29-17, 05:52 PM
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I have never seen a control board perform out of sequence before.
I was leaning towards a delayed igniter turn on but the times listed are too short which means the board is bad.
 
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Old 11-29-17, 07:10 PM
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Other possibility is that someone modified the wiring. Tried bypassing a pressure switch and attached it to the gas valve?
 
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Old 11-29-17, 09:18 PM
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Sounds like a way to burn down a house. I would never recommend Hot wiring a gas valve. It would always shoot out gas.
 
  #9  
Old 12-01-17, 04:31 PM
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Any updates here on your repairs?
 
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Old 12-04-17, 04:34 PM
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Thank you to everyone who took time to post! And, sorry for delay in reply - went out of town over the weekend.

Turned out to be an under-performing hot surface ignitor!

Here's what I did:
  • I called the control board manufacturing and was surprised when their tech took time on the phone to help me diagnose the signals. One of the first things we checked was the 120 volts on the HSI output lug at the proper time - which was confirmed.
  • And, we confirmed that the ignitor was passing current (i.e. not throwing a control board error which, for example, would happen if it had a crack) which is why the control board went ahead and opened the gas valve, even though visually it looked like something was wrong (i.e. ignitor was not glowing at all, or only glowing a little.)
  • Through a bunch of patience in waiting for the ignitor to thoroughly cool down between each attempt, I confirmed, and was able to replicate on each try, that the ignitor was heating up on each first attempt, but not to full or high enough temperature, and the residual heat left-over from first try, was allowing it to reach full or high enough temperature on the second or subsequent attempts.
  • As a result, I replaced with a new ignitor, and now the furnace starts-up correctly first-time, every-time.
Thanks again everyone!

Ralph George
 
  #11  
Old 12-04-17, 06:01 PM
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That is something new. Thanks for the update.
 
 

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