Suburban SF-20 furnace wont stay lit
Over the weekend, I ran the furnace a couple of times. Whenever there was actual combustion, I'd get a pretty good whistling noise. Figured I had some debris in the combustion chamber. Got it h...
Forum Discussion
Some Suburban heaters use the same circuit board as my Attwood.
From the time the Thermostat calls for heat
1: Blower starts (Working)
2: Sail switch closes (Working)
3: Gas valve opens and ignightor starts (Working)
4: Gas ignites (you hear it light so working)
5: Thermocouple heats (Working, since it is burning)
6: Control board looks for .480 volts from thermocouple (Suspect)
5: Absent .480 volts control board shuts it down.
Possible issues.
Thermocouple, Defective or dirty enough that it does not heat up in time.
Thermocouple/control lead: Poor connection causing low voltage delivery.
Control board: Defective
On my Attwood they use a SINGLE WIRE for both Ignition (Roughly 1,000 volts Peak based on the spark gap) and flame detection (less than 1/2 volt) Now imagine what would happen if the change over from MAKE SPARKS to Is it hot? Went flakey and the detector chip got hit with one of those killovolt peaks instead of the less than 1/2 volt it loos for.. it would become a Popped tart.
I replaced my $250 dollar control board with a $100 dollar Dinosaur board. (108 including S&H) and I will tell you a few things about Dino Boards.
First: I am trained as an Electronics technician with some engineering training as well. Also over 40 years as a Licensed Ham Radio Operator (WA8YXM, original issue 1968)
The first thing that struck me when I opened the box that Dinosaur board was in was the QUALITY of the unit, All the solder joints looked first rate, The traces were heavier than on the Attwood board and it just gave me a feeling of QUALITY the Attwood OEM board did not.
Then I looked closer.. I do not know for a fact that what I described above happened. But on the DINOSAUR board there was a device (Gas discharge tube) that did not exist on the Attwood board.. From it's location on the board (next to the connector for the wire mentioned above) I suspect it is there to prevent just the type of failure I think happend.
So.. Test everything, but if you end up replacing the control board.. Go with Dinosaur.. They are 1st rate.
From the time the Thermostat calls for heat
1: Blower starts (Working)
2: Sail switch closes (Working)
3: Gas valve opens and ignightor starts (Working)
4: Gas ignites (you hear it light so working)
5: Thermocouple heats (Working, since it is burning)
6: Control board looks for .480 volts from thermocouple (Suspect)
5: Absent .480 volts control board shuts it down.
Possible issues.
Thermocouple, Defective or dirty enough that it does not heat up in time.
Thermocouple/control lead: Poor connection causing low voltage delivery.
Control board: Defective
On my Attwood they use a SINGLE WIRE for both Ignition (Roughly 1,000 volts Peak based on the spark gap) and flame detection (less than 1/2 volt) Now imagine what would happen if the change over from MAKE SPARKS to Is it hot? Went flakey and the detector chip got hit with one of those killovolt peaks instead of the less than 1/2 volt it loos for.. it would become a Popped tart.
I replaced my $250 dollar control board with a $100 dollar Dinosaur board. (108 including S&H) and I will tell you a few things about Dino Boards.
First: I am trained as an Electronics technician with some engineering training as well. Also over 40 years as a Licensed Ham Radio Operator (WA8YXM, original issue 1968)
The first thing that struck me when I opened the box that Dinosaur board was in was the QUALITY of the unit, All the solder joints looked first rate, The traces were heavier than on the Attwood board and it just gave me a feeling of QUALITY the Attwood OEM board did not.
Then I looked closer.. I do not know for a fact that what I described above happened. But on the DINOSAUR board there was a device (Gas discharge tube) that did not exist on the Attwood board.. From it's location on the board (next to the connector for the wire mentioned above) I suspect it is there to prevent just the type of failure I think happend.
So.. Test everything, but if you end up replacing the control board.. Go with Dinosaur.. They are 1st rate.
