ignition controller hs780-785

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  #1  
Old 01-15-03, 02:24 PM
rac8006
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ignition controller hs780-785

I have a problem with the ignition controller on my furnace. It has a tendency to keep the glowbar glowing for a long time. The furnace maintains the temperture but the globars don't seem to last more then a year or two. So I decided that the hs780-785 controller needed to be replaced. I bought a new one and installed it as to the directions and it won't keep the gas on for more than 2 seconds. According to the part number hs780-34NL-306A it should keep the gas on for 6 seconds.

Any ideas as to what may be wrong?
 
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  #2  
Old 01-15-03, 03:14 PM
bigjohn
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Your new module is local sense. Local sense means you have to have an igniter with an intregal flame rod. Does your furnace have a remote sensing flame rod? IOW- a flame rod mounted on the burner some distance from the igniter? If so, then you need a remote sense module. The L in the model # would be an R. if you have local sense, then make sure the flame rod is clean and all the ground connections are clean and secure.
 
  #3  
Old 01-15-03, 04:38 PM
rac8006
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hs780

The old and the new controller have the same number. This unit uses a glowbar as the ignitor and the flame sensor. The old unit will leave the glowbar on for about 6 seconds after the gas is turned on. At this point the flame is present. As the glowbar stops glowing the flame keeps it hot.

ON the new unit it barely turns on the gas and then cuts it off.
Shouldn't the new unit at least keep the gas open for 6 seconds?

Both units are the HS780-34NL-306A but the part number of the old unit is 100-00812-12 and the new one is 100-00812-31.
 
  #4  
Old 01-15-03, 09:37 PM
bigjohn
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Yes, the 06 means a 6 second trial for ignition. Take your voltmeter and check the voltage going to the igniter. If it quits in 2 seconds, then take the module back, it's defective. I don't know the significance of the non Robertshaw part numbers. Honeywell makes a universal Hot Surface Ignition module that will repalce yours. I checked the cross reference. The difference is the HW will have a 7 second trial for ignition. The part # is S8910U.
 
  #5  
Old 01-16-03, 03:15 PM
rac8006
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Thanks for the information. I thought that the module was bad. But my friend who is in heating and cooling dosen't think that the module is bad. He said the problem was that the flame wasn't getting over to the flame sensor fast enough. I tried to explain to him that 2 seconds was to quick. He talked to his supplier and they made some comment about a field upgrade that adds a flame sensor on the other side of the pilot. But I don't think that is my problem

I've been using the old module for the last couple of days and its holding the temp at 66 degrees which I have it set to. I'm beginning to think that I may have a ground problem. Today I watched the glowbar glow for a long time. I turned it off a couple of time but it didn't turn on the gas. So I was touching the junction box that has the 24v transformer and it started. Later I went down to check on it and the next time it started if worked ok. I need to keep an eye on it for awhile.

I really appreciate you input.
 
  #6  
Old 01-16-03, 05:02 PM
bigjohn
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The comment about a remote flame rod is dandy fine, but, right away, you can tell they are not thinking because your application is local sense not remote. I think you mean the other side of the burners not the pilot. You don't have a pilot, do you? Make sure all the ground connections are clean and tight. The HW module can handle local or remote sense.
 
  #7  
Old 01-21-03, 12:30 PM
rac8006
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ignition control

Well it seemed to work for almost a week. Last night it stopped again. All I had to do was turn the furnace off then on. It worked for awhile. The problem of the glow bar glowing and not turning on the gas seems to be back.

Is there any kind of feed back from the glow bar while it is glowing? Or is the 30 second delay for the gas to be turned on a fixed time? I'm curious as to why it would work for a week then start acting up again.
 
  #8  
Old 01-21-03, 03:53 PM
bigjohn
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No feedback- it's a timed circuit. Now, what's been working for a week?- the old one or the new one? I owe you an apology. I re-read yours posts and realized I missed this first time around. If both the old module and the new one are the same part numbers, they both have a 34 second warmup time for the glow bar. By replacing, you haven't really gained anything. Maybe you should just put the old module back in and keep a spare igniter handy. Make sure all the ground connections are clean/tight.
 
  #9  
Old 01-21-03, 05:47 PM
rac8006
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hs780-785

The old one has been working for the last week until last night. The glowbar is ok. Its the HS780-785 that sometimes won't turn on the gas. I've checked and the 24vac is not supplied to the gas valve. I don't understand why the control will turn on the gas in 30 seconds sometime but not all the time.

The problem I ran into when I changed to the new unit is it will not keep the gas turned on for more than two seconds.
 
  #10  
Old 01-21-03, 06:13 PM
bigjohn
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No voltage at the gas valve but the glow bar is lit and the time delay has elapsed? Might be time to consider the Honeywell module. Go to http://hbctechlit.honeywell.com Click accept, on the next page, select model & all literature and type S8910U into the search bar.
 
  #11  
Old 10-22-08, 06:31 PM
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Question main burner not working

I got a most same problem of my furnace, glow bar is light around 30 seconds and then valve have a click sound for gas pass. flame like pilot also lite, but only 3 or 4 seconds the valve shut off. main burner not working.
i have check some wire connections seems nothing wrong, does means need a new ignition control module?
please help....
 
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