"Glow plug" won't glow...

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Old 10-01-06, 07:55 AM
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"Glow plug" won't glow...

I have a little HVAC experience, but not as much as I would like... Anyways, I have a RUUD Silhouette Gas furnace model # UGPJ-0702008800 and the "glow plug" won't glow. I have already replaced the "glow plug" and still no dice. The exhaust fan is coming on so I think it may be a sensor that senses the "glow plug" heat or else the gas valve??? Not really sure... hope someone can help. Thanks in advance for your help...
 
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Old 10-01-06, 09:14 AM
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Hot Surface Ignitor (HSI)

The HSI is not connected to the gas valve UNLESS the furnace has a Honeywell Smartvalve. Use a voltmeter to check for 120 volts across the terminals on the ignition control all the way thru an ignition cycle. If you get 120 volts, the ignitor or wires to it ar bad.
 
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Old 10-01-06, 12:00 PM
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Still no luck...

Thanks for the reply, I tested the wires coming into the "glow plug" and no voltage. I ran the same test on the identical unit that I have in the attic right next to it and it did have the voltage. When I ran the test on the good furnace, I heard a click on the main circuit board and then the wires leading to the "glow plug" registered 120 volts. However, when I ran the test on the bad one, there was no clicking sound on the board and thus no voltage. Is there another component in the ignition circuit that has to close in order for the circuit board to send the voltage or am I going to have to replace the whole circuit board??? Thanks again...
 
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Old 10-01-06, 12:04 PM
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Whoops

Sorry, the gas valve is a Honeywell, but does not have any marrkings stating "smart valve." Not really sure on how to tell if its a smartvavle or not...
 
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Old 10-01-06, 04:31 PM
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Hsi

If you got 120 volts, no need to worry about the SmartValve. The ignitor used on them is 24 volts.

Since the exhaust blower is working we can take that out of the picture. There should be a disk looking switch somewhere with one or two hoses on it & a couple of wires. This is a draft proving switch. When you start the furnace, give that switch a firm tap or two with a screwdriver handle. The have a habit of sticking over the summer. If that doesn't work, take the hoses off & blow thru them. Sometimes they can become plugged. If all of this fails, take the exhaust pipe down & look thru it checking for any kind of obstructions.
 
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Old 10-03-06, 06:53 AM
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Still no dice...

I found the switch and gave it a tap and no luck. I pulled the hose off and blew through it and even took the exhaust pipe down and no luck. Could it be something else? Thanks again for your help.
 
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Old 10-03-06, 06:26 PM
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Pressure switch

Normally there are two wires going to the pressure switch. With those wires disconnected & no call for heat, check continuity across the terminals. Initiate a call for heat & monitor the continuity. If continuity changes (open to closed or closed to open) it would seem the swich is good & the problem is elsewhere. If you can attach or link to a wiring diagram it would help.
 
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Old 10-15-06, 09:29 AM
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Smile You got it!!!! PROBLEM SOLVED!!

Thank you so much!!!! I checked the switch and it continued to have an open circuit when heat was called for and the exhaust fan activated. I ran the same test on my other unit and the switch closed the circuit when heat was called for. I took the switch off the good unit and put it on the one I am reapiring and it worked like a charm. Now I just need to order the new switch. I've looked on the internet and can't really find much. Does the switch go by a different name ...maybe "pressure switch, air proving switch, etc..." Also, is this a standard generic switch or is it most likely a "RUUD" specific switch. If you can recommend a good online parts place, or maybe a good store in the Atlanta area. I would really appreciate it. Once again, thanks (you saved me a bunch of $$$$).
 
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Old 10-15-06, 03:22 PM
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Pressure switch

The big thing with pressure switches is the pressure at which the operate. If you get lucky, yours will be marked with a pressure rating usually in inches of water column. (in. w.c.)

There are several names including air proving switch.
 
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