Hey All,I still have my Jazz after all these years and it's been fantastically reliable -- until now.Recently the furnace, a Suburban SF-35F, won't light. Here is what I know thus far:Voltage at battery is 12v.Propane tanks are full and stove (immediately above furnace) runs steady.Thermostat seems to be sending "call for heat", as I can hear a relay clicking at the furnace when it's supposed to turn on.Fuse to furnace is fine.To be fair, I haven't done ANYTHING to this furnace in terms of periodic maintenance since I purchased the rig new -- there is NO access to anything regarding the furnace.I would ordinarily check the sail switch (etc.), but I can't reach it without pulling the furnace out of the cabinet, and I don't have a bench set-up to test the furnace out of the cabinet.What should I check next and do I really need to pull this wretched thing out of the cabinet to troubleshoot it?Thanks!

When I have anything 12 volt that is not working properly I always check the ground first.

I would bet on it needing cleaning.Need to access it and either blow it out good with compressor or use a strong vacuum.Either dirty sail switch or burner electrode.Does the fan run? If not tripped circuit breaker in furnace.

12V is LOW voltage......should be up around 12.4V at least.When you hear the 'click' does the fan come on and blow air??Ain't nothing going to happen until that occurs.Get you battery voltage up.

Agree, if voltage is 12.0, that is LOW. If it is really that low, start by charging battery.But, tell us how far into the heat cycle it gets:Thermostat signal to PC board.Fan starts. Sail switch closes.Gas valve opens and igniter sparks.Furnace runs.

There is a process involved in the furnace working, I will try to type it as best I recall.T-stat calls for heat1: Control board starts blower2: Blower comes up to speed and moves enough air to 3: Close the sail switch4: Control board opens gas valve and 5: Starts the ignighter sparking.6: FLAME ON7: Thermocouple heats up and starts generating about .480 volts8: Motor board shuts down ignighter and looks for .480 volts from thermocouple9: Operation continues or not depending on 8IF NO voltage: go back to 1, twice, if still no signal from thermocople lock out.If yes: Flame continues till either the OVER TEMP sensor opens, in which case it is cut off till the furnace cools some.. AIR flow is lost or The T-Stat says "ENOUGH already"I have never done an over temp so I think it will re-start when it cools but not sure.When the T-stat says "ENOUGH" the flame is cut off,, then after a bit the blowerPossible issues.Low battery, bad sail switch, old tired blower motor, dirty blower or air passage, bad control board, (If it never lights) improper spark gap (I have seen this on every furnace I've worked on, both in my RV and my parent's sticks & Bricks). and more.But we need to know how far down the process it goes before it fails.

ZagiFlyer

Explorer

Dec 31, 2013

Suburban SF-35F won't light

Hey All,

I still have my Jazz after all these years and it's been fantastically reliable -- until now.

Recently the furnace, a Suburban SF-35F, won't light. Here is what I know thus far:

Voltage at battery is 12v.
Propane tanks are full and stove (immediately above furnace) runs steady.
Thermostat seems to be sending "call for heat", as I can hear a relay clicking at the furnace when it's supposed to turn on.
Fuse to furnace is fine.

To be fair, I haven't done ANYTHING to this furnace in terms of periodic maintenance since I purchased the rig new -- there is NO access to anything regarding the furnace.

I would ordinarily check the sail switch (etc.), but I can't reach it without pulling the furnace out of the cabinet, and I don't have a bench set-up to test the furnace out of the cabinet.

What should I check next and do I really need to pull this wretched thing out of the cabinet to troubleshoot it?

Thanks!

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Suburban SF-35F won't light

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