Carrier Furnace Intermittent Start

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Old 10-12-09, 10:10 AM
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Carrier Furnace Intermittent Start

I have a 15 years old Carrier Weathermaker 8000 58WAV090 furnace. It runs on natural gas. There is no standing pilot light. It uses hot surface ignition (HSI) system. The gas valve is White Rodgers 36E98-202. It has M, C & P terminals. The M and P are connected together. Two wires coming from the control board to the C and M-P terminals. I also cleaned the flame sensor.

It goes through the start flame sequence:
1. purges the system with air,
2. turns on HSI - confirmed by red hot ignitor
3. turns on gas valve - confirmed by 25.5Vac on C and M-P
4. flame confirmation

It went through step 1 to 3 without getting the flame. It will try 3 more times. It will lockout the system after the third try. I have to cycle the power before it will sequence these steps again. I can get it to full flame if I continue to cycle power. Usually after trying 5 - 6 cycles of these start flame sequence.

The control board does not have any LED or display to tell me the error code.

I came to the conclusion that the gas valve is no good.

I called the service tech last Friday to service it. First thing he said that he has not seen any gas valve with intermittent problem. Gas valve either working or NOT working - nothing in between. He went on to clean the HSI and moved the HSI closer to one of the gas nozzle. After that, he was able to demonstrated the furnace going to full flame on every try. He went away without replacing the gas valve.

My furnace is doing the same thing for the past weekend. I need your advice. Thanks
 
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Old 10-12-09, 10:31 AM
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What do you mean by "flame confirmation"? Is the main burner lighting, then shutting off? if so, after how long a period of time?

You mention that the HSI gets red. Typically, it should get white hot to light the gas. This suggests that either the HSI is defective and needs to be replaced (likely, if I'm interpreting your comments correctly) or that the HSI isn't getting 120VAC applied to it.

Check the voltage to the HSI with an AC voltmeter to check that. That's a fairly low probability, but it could be a bad relay or other defect on the ignition control.

And if you have a bad HSI ---get two to have a spare for the next time a HSI problem crops up.
 
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Old 10-12-09, 03:30 PM
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Originally Posted by SeattlePioneer View Post
What do you mean by "flame confirmation"? Is the main burner lighting, then shutting off? if so, after how long a period of time?
When it get the flame and the flame sensor confirms it, the flame will stay on until the thermostat turns off the gas valve.

You mention that the HSI gets red. Typically, it should get white hot to light the gas. This suggests that either the HSI is defective and needs to be replaced (likely, if I'm interpreting your comments correctly) or that the HSI isn't getting 120VAC applied to it.

Check the voltage to the HSI with an AC voltmeter to check that. That's a fairly low probability, but it could be a bad relay or other defect on the ignition control.

And if you have a bad HSI ---get two to have a spare for the next time a HSI problem crops up.
The HSI is bright red in color. I have not measured the voltage to the HSI. But the service tech touched the wires with a tester and it beeps to proved that 110VAC was present at the HSI. I am going to buy a HSI tomorrow to eliminate the HSI problem before I call the service tech again to change the gas valve.

Edit 1:
I may use a 11" long fireplace matches to light the flame after the HSI grows red. This may prove that the HSI is not hot enough! Is this safe to do it so?
 

Last edited by embguy; 10-12-09 at 04:08 PM.
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Old 10-12-09, 04:26 PM
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If the main burner stays on until shut off by the thermostat, what's the problem?


I'm apparently not understanding you.
 
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Old 10-12-09, 04:37 PM
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Sorry for confusing you.

Most of the time, it went from steps 1 to 3 without getting a flame. Usually, it took 5 - 6 tries before the furnace completing the step 4.
 
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Old 10-12-09, 04:49 PM
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With a hot surface ignition system, the main burner gas is turned on and should light promptly. If it fails to light, you want the gas to shut off, not to remain on and unlit.

So the ignition control module has a way to check to see if the main burner lights. On the side opposite the hot surface ignitor, you should see a small rod sticking up through the burners with a wire going back from it to the ignition control module.

That rod is the flame detector. It can get coated with oxides that impair it's ability to detect the presence of the main burner flames, which then causes the ignition control to shut off the burners and restart the ignition sequence as you describe.

This is the most common reason for the problem you describe.

So I'd remove the flame detection rod and clean it with a wire brush or some fine sandpaper. It doesn't take a lot.

Then reinstall it and try it again.
 
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Old 10-12-09, 05:10 PM
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I cleaned the the flame sensor.

Most of the time, there is no flame when 25.5Vac was applied to the gas valve. I heard a click sound and no flame. But after a few tries, it got the flame and the flame stayed on until the thermostat turns off the gas valve. Therefore, it is not the flame sensor problem. This is why I think that the gas valve is the problem (stated in my first post) because I assumed that red hot HSI is a working HSI. Can I use an 11" fireplace matches to light the furnace after the HSI grow red? If the flame comes on, the HSI is at fault. If not, the gas valve is the problem. Do you agree?
 
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Old 10-12-09, 05:15 PM
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Is the main burner gas actually turning on when the 24 VAC is applied, or is the gas only turning on intermittently?


If you aren't getting main burner gas when the 24VAC is on, you probably have a bad gas valve.

If the gas does come on reliably, it should be lighting off the HSI each time.
 
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Old 10-12-09, 05:26 PM
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The furnace got full flame once for every 5 -6 tries. It is intermittent.

But you planted the seed in my head that the HSI may not be hot enough! But I can feel the HSI heat at the edge of my furnace.

Using a fireplace match can isolate the HSI problem. Do you agree?
 
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Old 10-12-09, 06:32 PM
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I recommend safety glasses for your test.
 
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Old 02-14-13, 01:17 PM
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Wow! This is a bit dated thread but the problem is with the solenoid on the gas valve. Mine has been giving me intermittent trouble for a few years now so what I've been doing is waiting until after the igniter glows white hot, a few seconds will pass then you will hear the click of the relay which energizes the solenoid valve but the plunger is sticking or the solenoid is too weak to open it but that's when I tap on it and most of the time it will fire right up. I'm finally getting around to ordering a replacement for it as the frequency of this problem is a bit much at this point. Good luck to those of you who continue to encounter this problem.
 
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