Amana AMH95 not igniting

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Old 10-16-16, 06:29 PM
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Amana AMH95 not igniting

Hi everyone,

I thought I was doing well this year by testing the furnace before it got cold, but it worked for a few days and has now stopped.

Here's the pattern I see:
1. Induced draft blower turns on for ~10 sec
2. Igniter glow for ~5 sec
3. Igniter glow goes off
4. Blower continues for ~10 sec, then cuts out and immediately restarts

This pattern repeats 3 times and then stops. Diagnostic LED flashes once, which my manual says "Furnace lockout due to an excessive number of ignitions retries"

I don't hear any click when the igniter is glowing, so I'm guessing the gas valve or controller board is the problem. But I'm out of my depth at this point. I know electronics and can use a multimeter but don't have much appliance experience.

Thanks for any help. I can tell from browsing the forum that this is a fantastic resource.
 
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Old 10-16-16, 09:23 PM
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Welcome to the forums.

Does the igniter only glow for +/- 5 seconds every time it starts ?

If it's the same amount of time every time then it sounds like the control board. The igniter should glow for close to 30 seconds before the gas comes on and the burner lights.

However..... based on your partially posted model number it looks like you have a two stage furnace with dual pressure switches. This IS NOT an easy furnace to work on. It is fairly involved and sophisticated.

I posted the link for the manual below. You'll need to change the .cfm extension to .pdf
On page 179 it discusses the coil cover pressure switch. You'll need to check the tubing for clogs or water. It needs to be clean.

alpine home air/viewresource.cfm?ID=2470
 
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Old 10-17-16, 12:31 PM
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The ignitor typically needs to heat up for thirty seconds or so to get hot enough to light the gas.

Then the circuit board should turn on the main burner gas and the main burners should light off the HSI. If the main burners fail to light, the circuit board should shut off the gas after three seconds or so.

Is that main burner gas being turned on as I describe?

I never saw a circuit board that failed to turn on the HSI for the proper time, if it was turning it on at all. But five seconds sounds like much too short a time for the HSI to get hot enough to light the gas.
 
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Old 10-17-16, 06:01 PM
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Thanks for the input. I went to get more accurate timings for you (I was just guessing before...sorry!) and it lit up just fine. So it looks like an intermittent situation.

The complete model number is: AMH950904CXAD

The blower runs for 20 seconds, then the glow comes on.
The gas turned on after 15 seconds of glow and it lit fine, with the main fan coming on after the normal heat-up period.

When it was failing, the gas never came on. The igniter went dark and then the whole cycle was repeated. I don't have an accurate measure for how long it waited, when it was failing, before turning the igniter off. But I feel like it was pretty similar to the 15 sec I just measured when it worked fine.

Any suggestions for what to do? I know intermittent problems are the worst to debug!

many thanks,
Rob
 
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Old 10-17-16, 09:04 PM
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<<When it was failing, the gas never came on. >>


Carefully observe the sequence of events that occurs when the furnace lights up normally.

When it fails to light again, that will give you a reference which will help you identify the problem.

Very likely the circuit board is failing to turn on the power to the gas valve, which would require replacement of the circuit board/ignition control module.

You might practice observing and measuring that 24 VAC power being switched on when the furnace is operating normally, again so you can compare it with what happens when it wont light.

An intermittent problem such as you describe is very likely a part which is going bad and will quit working altogether before long. So be prepared!

Shop around for a part to buy or order NOW, even if you don't want to buy it now.
 
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Old 10-24-16, 10:38 AM
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Thanks for the advice. I did take down part numbers and start to explore where I could get them.

In the meantime, it's changed behavior. It still doesn't light reliably, as before. I can eventually get it to light with several tries. Most of the time it fails to have any ignition after the HSI has been glowing the requisite time. But after a few tries the gas comes on and it lights.

I had thought that it would keep the flame fine after eventually getting it lit (so that I could at least get the house up to temperature once before it then ran into the lighting problem again and locked out ).

But now I've realized that the flame is going out even while there's still a call from the thermostat (i.e. the house is still not up to temperature). I noticed first that while heating the blower would cut off for a second or two and then kick back on. That was odd. But now while it's heating the blower goes off and stays off -- I go to check it out and there's no flame (I'm assuming it's locked out but I can't say I checked the LED blink code at that point).

Service guy coming tomorrow. So I'll hang out with him and try to learn something. Anyone want to guess what he'll find or offer any other advice?

--Rob
 
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Old 10-24-16, 10:56 AM
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Is the gas valve being powered?
 
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Old 10-24-16, 11:09 AM
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Is the gas valve being powered?
I haven't checked yet. I don't have a clamp ammeter. Should I try to stick VAC multimeter probes into the back of the white plastic three-wire connector to look for the 24 VAC? I'm guessing I can't test it while disconnected because this thing is likely sophisticated enough to check for the valve being connected?
 
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Old 10-29-16, 12:09 PM
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not what I expected!

All's well now, but it wasn't what I expected.

It was the first thing the service guy checked: a partially blocked drainage line from the flue. That led to water draining into the inducer and it was sloshing around in there, cutting its flow. If I had run it with the cover off, I'm pretty sure I would've heard it -- it was quite obvious then.

The blockage was in a 3/8" 45 degree plastic elbow (my guess at the size). He cleaned that out at the sink. Then he pulled the inducer and dumped out the water. Assembled it back and all is well.

For what it's worth, he said that he almost never sees a faulty gas valve (maybe twice in 5 years) and quite rarely sees a problem with a control board, though that happens more often than a gas valve.

Not sure the cause of the blockage, though last year a spider had built a nest in the last burner, so I'm suspicious of an arachnid-induced inducer fault!

Anyway...thought I'd report back for the record. Thanks for all of your help!

--Rob
 
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Old 10-29-16, 01:23 PM
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<<The blower runs for 20 seconds, then the glow comes on.
The gas turned on after 15 seconds of glow and it lit fine, with the main fan coming on after the normal heat-up period.

When it was failing, the gas never came on. The igniter went dark and then the whole cycle was repeated. I don't have an accurate measure for how long it waited, when it was failing, before turning the igniter off. But I feel like it was pretty similar to the 15 sec I just measured when it worked fine.

Any suggestions for what to do? I know intermittent problems are the worst to debug!>>



Thanks for reporting back. Apparently you were having the pressure switch open intermittently, which interrupted the ignition sequence.

<<For what it's worth, he said that he almost never sees a faulty gas valve (maybe twice in 5 years) and quite rarely sees a problem with a control board, though that happens more often than a gas valve.>>


That's all true.

<<It was the first thing the service guy checked: a partially blocked drainage line from the flue. That led to water draining into the inducer and it was sloshing around in there, cutting its flow. If I had run it with the cover off, I'm pretty sure I would've heard it -- it was quite obvious then.>>


Sounds like you found a competent and honest repairman. Call him again when you need help!

<<The blockage was in a 3/8" 45 degree plastic elbow (my guess at the size). He cleaned that out at the sink. Then he pulled the inducer and dumped out the water. Assembled it back and all is well.>>


A weakness of condensing furnaces is that they can accumulate algae or other sludge that grows in the warm condensate water.
 
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Old 10-31-16, 11:33 AM
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Sounds like you found a competent and honest repairman. Call him again when you need help!
Yes, these guys have always treated me very well. They're willing to explain everything along the way. They showed me how to clean the flame sensor myself. When they came out to look at the A/C, they checked the inducer on the furnace, noted a slight bearing problem, told me it was their most common failure and went ahead and replaced it under warranty before it failed.

--Rob
 
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