jaybird6973
Member
Furnace was working great. Fan comes on and it doesn't even stay on long enough to try to ignite and shuts down. Have to pull the unit to check the sail switch unless someone has some advice.
Suburban furnace quit working
- Thread starter jaybird6973
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Rene T
Site Team
Do you have propane and is the valve open and not closed. Does your cooking stove work OK?
jaybird6973
Member
Turned off thermostat for about an hour and when I turned it back on it worked fine all night... weird.
Kirk
Well-known member
It would help to know which model of Suburban furnace you have. The age of that furnace would also help. In my experience a failing sail switch is rare but can happen. The actual voltage in your 12V system is what determines how fast the blower runs and if that voltage is less than 11V (actual measered with a quality digital meter) then the blower may not turn fast enough to close the sail switch and that would cause it to never open the propane valve or attempt to ignite. If the voltage falls below 11.5V it will not close the sail switch. If you were connected to shore power that shouldn't happen, but only a meter reading when it is happening would tell us for sure. Have you serviced the coach batteries recently? Is the electrolyte at the proper level?
The symptoms as you describe them would fit with battery voltage having been low and then recovered. Another possible cause would be a failing ignition probe or bad connections to it.
The symptoms as you describe them would fit with battery voltage having been low and then recovered. Another possible cause would be a failing ignition probe or bad connections to it.
jaybird6973
Member
Furnace is a Suburban SF30 model and I am connected to shore power. I think I may have tweaked the system by changing one of my battery connections to a wing nut and forgot to turn of furnace. Not sure if this caused the problem. Hate it when something quits working and then starts working again.
Kirk
Well-known member
If you look in the operator's manual it states that if the furnace fails to light after 3 attempts, the furnace will go into lockout and the blower will continue to run for about 5 minutes, then turn off and the thermostate will have to be turned off and then back on to restart.
Have you done any troubleshooting or taken any meter readings? Here is a copy of the Suburban Service Manual that you can download.
Have you done any troubleshooting or taken any meter readings? Here is a copy of the Suburban Service Manual that you can download.
I would not think that would cause any problems unless something pretty unusual happened. If the frunace was off at the thermostat at the time or if on but not calling for heat, there would have been no power to the furnace circut board. To totally isolate it you would need to remove the fuse that supplies it. If you disconnedted the negative battery post first and reconnected it last, there is almost no chance that you damaged anything.
jaybird6973
Member
Update: replaced the propane regulator with a Marshall Excelsior high flow regulator with high flow pigtails and it worked fine for a month or so. We don't use it that often, but when we wanted to it worked great. All of a sudden it turns on as regular and then ignites, stay lit for a minute or so and then shuts down. Switched propane tanks and over to the other pigtail and no change. Checked the high temp limit switch and it is working fine, and even out a jumper to bypass it and the same thing happens... it shuts down after about a minute of working fine.
Anybody have any suggestions?
Anybody have any suggestions?
OldWEB
Well-known member
The manual link that Kirk seems a little dated, how old is your SF-30?
SF-30 Service Manual
With links on the right to more specific SF-30 models.
One item it could be is low DC input voltage, which could reduce fan speed/sail switch.
Another is the flame sense circuit/adjustment.
You will have to read up on these.
Good luck!
SF-30 Service Manual
With links on the right to more specific SF-30 models.
One item it could be is low DC input voltage, which could reduce fan speed/sail switch.
Another is the flame sense circuit/adjustment.
You will have to read up on these.
Good luck!
Kirk
Well-known member
When the propane ignites, does the ignition probe stop sparking? If it doesn't then it isn't detecting the heat from the burning propane. If it does burn for a full minute, that is longer than would normally be the case with a sensing failure but you may still want to consider that probe. At least try cleaning and tightening the connection to the probe as the sensing signal is in the micro-volt range and can easily be lost.
Gary RV_Wizard
Site Team
When you say "shuts down", I'm assuming you mean the burner shuts off but the fan continues to run for a minute or two before it too shuts off. If that's the case, loss of the flame sense signal or a high limit fault is the only explanation. You eliminated high limit (and it didn't run long enough for a high limit fault anyway), so that leaves the flame sensor in the igniter electrode or its electrical connection to the control board (see Kirk's reply).
jaybird6973
Member
Ok, thank you all for the advice. I was afraid of that and now the daunting task of pulling it out of the cabinet. It makes sense that it is the the flame sensor as it acts that way... runs normal enough but probably doesn't realize it has a flame and goes out.
jaybird6973
Member
Yes, it does stop clicking by the way. It starts clicking again as soon as I hear the flame go out, but does not light again as it must shut the gas valve down or something.
Kirk
Well-known member
I just noticed that link that I sent didn't work so use this one instead.
The sparking would indicate that it sensed a loss of the heat from it burning. That triggers the attempt to relight the furnace. When this happens, have you ever been where you can see if the flame actually went out?
jaybird6973
Member
I go out by the exhaust to listen and feel the flame go out. You can tell by the sound and by the moisture change in the exhaust. It immediately attempts to relight by the clicking of the ignitor, but after the 3 attempts it stops and the motor runs the shutdown cycle.
Kirk
Well-known member
That is a clear indication that the system did lose the return signal from the ignition probe and that it was due to the flame going out. The most probable reason that I can think of would be a loss of propane supply. If I am right that would leave 2 prime suspects, the supply valve or the propane regulator. As a next test, I would light a burner on the stovetop and let it burn for several minutes, then with it still burning start the furnace and see if the symptoms remain the same and what that burner's flame does at the same time. If the regulator is the problem it should show in the stovetop burner's flame as well, if the furnace lights at all.
jaybird6973
Member
I will test that, but I did just replace the regulator with a high flow regulator and new pigtails to match. It is how it was acting prior to the replacement though.
Gary RV_Wizard
Site Team
My guess is that there is a problem with the air+gas mix, which usually means either an impediment in the exhaust or air intake tubes or a leak in the gaskets around them. Most people think LP gas as highly explosive, but in fact it is extremely fussy about having an exact air/fuel mixture for combustion. Rust flakes, insect webs or nests, or anything that disrupts the pre-tuned in/out flow can cause the burner to flame-out. And be unable to re-light.
