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Old 10-07-2005, 12:05 PM   #1
1 Rivet Member
1992 34' Excella
Punta Gorda , Florida
Join Date: Sep 2005
Posts: 14
It's a cold furnance in winter

Started having some problems with the heater now that it's starting to cool off. Of course I did. Sometime back it would run once when it wanted to and others (USUALLY COLD MORNINGS) it wouldn't. The blower would come on but no heat. The sparker was doing fine which ruled out sail switch problems but no flame. Now the fan fails to come on. Sure hate to pull it out just before we leave but not sure what the problem could be. Sure don't want to hear control panel but gas valve problem could be fixed and I'd stlll have a little money left for fuel. Maybe.
It's a surburban heater in a 92' 34 excella that's in mint condition. Everything else works great and we're full timers heading back to Florida. Any ideas from this new family I found would be appreciated. Is this a great site or what???

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Old 10-07-2005, 12:37 PM   #2
Rivet Master
1975 29' Ambassador
Reno , Nevada
Join Date: May 2003
Posts: 1,351
For the DSI type furnaces it goes like this as best I understand things.

Thermostat calls for heat. Tells time delay relay which warms up quick and provides electricity to the blower. Blower starts moving air which activates the sail switch which tells the controller board its time to start the burner. The controller board activates the gas valve to get LP to the burner and hits the igniter to get it burning. When the burner starts, it changes the resistance between the igniter electrodes that tells the controller its OK to keep the gas coming else the controll will shut down the gas valve.

When the thermostat decides its hot enough it turns off voltage to the timer relay. The controller board sees this and shuts off the gas valve. After a few seconds, the relay finally relaxes and drops power to the blower and the furnace shuts down.

Now, if you are getting to the ignition phase but not getting the burner to light, it means no LP to the burner. First thing to do is to make sure LP is getting to the furnace OK. Then check the voltage across the gas valve so see if its getting the signal to open up at the appropriate time. If it gets the signal but there is no gas then the gas valve doesn't seem to be working as it should. If it doesn't get a signal, then the prime suspect is the controller board because getting a signal to the gas valve is its job.

And, as always, the diagnostics process is one of creative ingenuity. Hypothesis and possibilities I have suggested may or may not lead in the right direction for your situation. Good Luck. Have fun. Be careful and do it the safe way.

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Old 10-07-2005, 02:52 PM   #3
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Join Date: Dec 2002
Posts: 1,310
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If you follow Bryan's excellent advice, and discover it's the board (which I would suspect), I recommend the Dinosaur Universal Ignition Board (UIB). Putting "dinosaur" in the search box will explain why. Good luck.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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Old 10-07-2005, 03:16 PM   #4
Rivet Master
1975 29' Ambassador
Reno , Nevada
Join Date: May 2003
Posts: 1,351
The fan 50 plus board will shut down the fan if the burner fails such as an empty tank. good feature. It can be had for $100 or so if you look around.
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Old 10-07-2005, 07:24 PM   #5
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Darol Ingalls's Avatar
Join Date: Mar 2004
Posts: 411
Wern't pilot light furnaces great??? No electronics, no fridgid start-ups, and easy to trouble-shoot. Ah, progress . . . Darol
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