Problems with HSI (hot surface igniter)


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Old 03-08-10, 04:38 PM
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Problems with HSI (hot surface igniter)

Well I have a new HSI and it is not heating up. I tested where the harness for the HSI plugs into the gas valve and get 24 volts. As soon as the HSI is plugged in it looses the 24 volts. I've tested the HSI by sending power to it and it heats up and glows. Could the gas valve be bad or is there anything else I could test for? Thanks in advance.
 
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Old 03-08-10, 06:22 PM
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Post the make and model of this furnace.
 
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Old 03-08-10, 06:24 PM
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Hsi

From your description it sounds like you have a Honeywell SmartValve. Can you light the pilot with a bbq lighter once the warm up period reaches the end?
 
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Old 03-08-10, 07:35 PM
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Yes its a Honeywell.

The HSI does not even glow. It is a good part but when its plugged in I loose my 24volts. being sent to it. Im assuming since it will not warm up the gas valve will not open.

Im assuming since I can confirm 24 volts is being sent to the HSI besides when its actually plugged in could it be that when I do plug it in and loose my 24 volts could it be the load that causes my voltage drop. Or is there some sort of other signal wire or relay interrupting the 24 volts that im trying to get to the HSI.

I hope I explained this somewhat clearly im by no means a hvac expert and I appreciate any help.
 
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Old 03-08-10, 08:06 PM
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SmartValve

I'm no expert on SmartValves by a long shot but I'll try. You said you loose the 24 volts when you plug in the hsi. Where are you measuring the voltage?
 
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Old 03-08-10, 08:11 PM
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Originally Posted by Grady
I'm no expert on SmartValves by a long shot but I'll try. You said you loose the 24 volts when you plug in the hsi. Where are you measuring the voltage?

Im measuring where the HSI 3 prong harness harness plugs into the gas valve assembly. I'll unplug the harness to the HSI and measure 24 volts then plug it in and it goes to 0.
 
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Old 03-09-10, 08:05 AM
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Remember that if you test in series, you are going to loose the 24 volts if the circuit makes it's way to ground. The reason being is that the path of least restance is to ground and not through the resistance in the voltmeter.

You must be testing some male pin (which recieves the jack?) in the valve itself, that gives the 24 volts out of the valve, so that it can go into the HSI? Is that correct? Where are you able to test the HSI wire to find there are no volts when it gets plugged back into the jack? Is there antother jack connection for the HSI downstream toward the HSI? Or are you leaving the jack a tad ajar so that the jack both makes contact and you are able to touch the 24 volt pin at the same time?

Please explain real good on how you are making the test. Explain al the parts real good.
 
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Old 03-09-10, 10:47 AM
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Originally Posted by ecman51`
Remember that if you test in series, you are going to loose the 24 volts if the circuit makes it's way to ground. The reason being is that the path of least restance is to ground and not through the resistance in the voltmeter.

You must be testing some male pin (which recieves the jack?) in the valve itself, that gives the 24 volts out of the valve, so that it can go into the HSI? Is that correct? Where are you able to test the HSI wire to find there are no volts when it gets plugged back into the jack? Is there antother jack connection for the HSI downstream toward the HSI? Or are you leaving the jack a tad ajar so that the jack both makes contact and you are able to touch the 24 volt pin at the same time?

Please explain real good on how you are making the test. Explain al the parts real good.
Yes when the hsi is unplugged I test at the valve assembly where the 24volts is supplied and get 24volts. Now when the hsi is plugged in I am testing at the harness by pushing the leads to the multimeter into side where the wires come out of the hsi harness. Heres what I dont understand. I unplugged the hsi and where the power is supplied to the hsi I took a small 24 volt motor i had and hooked it up and it wouldnt run, but as soon as I took the motor off it went back up to 24 volts. I was just curious if the circuit board possibly may be bad in the valve assembly when there is an actual load put on it.
 
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Old 03-09-10, 03:24 PM
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Your test is okay. You are not in series.

Is your test meter set to a/c, the way it should be?

Is that 24 volt motor an a/c motor?

The HSI should actually be 120 volts.
 
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Old 03-09-10, 04:00 PM
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Meter is set to AC and little test motor is AC. The HSI is a 24 volt unit for this furnace.

I went and just tried wiggling the harness for the hsi while plugged in and it worked, but only for a few seconds. Im starting to think that the circuit board has a bad connection. I looked up SV9500 which is the part number for the smart gas valve and there seems to be an issue with these and there is a revision to replace that part with new part number sv9501.
 
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Old 03-09-10, 05:23 PM
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A 24 volt HSI. Huh. Funny they all aren't that, if that can get hot enough to work. Then again, maybe they have a worse record of having something burn out, I don't know.

Do you have something like a smart valve? If so, I replaced one on a gas water heater a couple years ago, for the same reason you have. Bad connection inside, that could light tehj W/H only by babysitting it and jiggling wires. After concluding it was not with the plug/jack, we broke down and paid the bucks to put in new one, and that fixed it. It looked like the area where it was bad might have been a separate replaceable part, but was told you had to buy the whole thing - gas valve and all.
 
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Old 03-09-10, 05:33 PM
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With a make and model number, I may be able to post a diagram to aid in the diagnosis of this problem.
 
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Old 03-09-10, 06:33 PM
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Yep its a smart valve.

Its actually my parents furnace and I dont have the make/model number off hand, but im going there and i'll post tomorrow. Thanks again everyone!
 
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Old 03-13-10, 07:10 AM
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Well it ended up being a relay soldered to the circuit board inside the smart valve. Seems to be a pretty common issue. I re soldered it and it seems to be working fine.
 
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Old 03-13-10, 01:30 PM
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Well, I guess a moral of the story can be that as long as a person is pretty sure where the problem is, and you are ready to buy the (expensive) new part, anyway. You may as well try to open it up and take a peek.

Glad I did recently with that inducer that simply had tar putty that relocated beween the blower wheel and housing, where the HVAC place wanted $202 for a new inducer assembly. I've done the same things that contain contacts and polished those back up to put the part back online. Same with making 2 bad AC condensor fan motors into one good one........for a few quick examples.
 
 

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