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American Standard/Trane Ignitor comes on, gas valve clicks, then fails to light

American Standard/Trane Ignitor comes on, gas valve clicks, then fails to light


  #1  
Old 10-26-19, 09:49 AM
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American Standard/Trane Ignitor comes on, gas valve clicks, then fails to light

First post here....

Been battling my furnace for the past month. Replaced controller board (White Rodgers 21V51U-843), and flame sensor so far. The furnace will light sometimes, but mostly, will retry then go into lockout.

I can finally reproduce the exact thing that it does. Now, have to diagnose and repair the issue. I've video recorded it numerous times so I could then check to see how its behaving

Here's exactly what happens....

1) Call for heat
2) Inducer runs at high speed
3) Inducer lowers to low speed
4) Ignitor comes on for its 17 seconds or so
5) Gas valve "clicks" but it fails to light (THIS IS THE ISSUE)
6) About 4 seconds later, the ignitor shuts off, and the system goes into purge mode (this is how the control board is supposed to work)

Then it will retry until lockout.

The new control board is working correctly as far as I can tell based on timings.

So no clue how to proceed. Could be the gas valve I guess, but not sure how to diagnose.
 
  #2  
Old 10-26-19, 10:29 AM
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What is incoming and manifold gas pressure?
The burners should be removed and cleaned, as fuel burning appliances need yearly maintenance such as this.
 
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Old 10-26-19, 01:21 PM
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Cleaning is a priority. Gas valves rarely go bad and if they do go bad.... they usually don't make any sound. Dirty orifices in the burner..... especially in the burner where the igniter is..... is a very common problem.
 
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Old 10-27-19, 05:24 PM
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Thanks for the replies. I'll give it a good clean. It seems pretty clear, but it can never be too clean.

I think it may have been a flaky ignitor ultimately, but still not sure. It did it again today, but this time, the ignitor failed to glow. Put multimeter on the leads, showed 120V when it was supposed to be turning on but it did nothing. I replaced it, now it seems to be behaving.

Roughneck, gas pressure is fine. Shouldn't have changed, just started acting this season.

Pjmax, I'll check out the orifices. I'm in northern Bergen county BTW
 
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Old 10-27-19, 05:43 PM
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Just to be clear, DO NOT clean the hot surface ignitor.
But the burner tubes, orifices and other parts of the burner require yearly maintenance and cleaning.
Output pressure of the valve can change and require adjustment. Itís not a device that you set it once and never check it again.
 
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Old 10-27-19, 06:04 PM
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Thanks Roughneck!! As far as the pressure valve, that makes total sense. Didn't think about it actually.

I've seen the warnings about not cleaning the ignitor, and I simply replaced the old one with a brand new one and it seems to have come back to life reliably. The original was a flat Silicon Nitride unit with a ceramic base. The new one is the universal White Rodgers replacement that looks like a rod and had a universal bracket that I adapted. I did order the correct replacement Silicon Nitride part though.

I've been battling it for a few weeks. The AC side had its own set of problems this summer, which hopefully, a new control board will rectify.
 
 

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