We're cold! Suburban SF-24 furnace failing in freezing temperatures

[EricSirianni]

My wife and I are living in our motorhome in the Philadelphia area and it's starting to get below freezing at night. The furnace(Suburban SF-24) works great all day but during the 3 coldest nights in the high 20's it has shut off while we were sleeping. When we finally wake up from the quickly dropping temperature, I switch the thermostat off and on and it normally starts back up but has a high pitched whine for the 15 seconds to a minute. I've never once heard that sound during the day.

A couple times throughout the night it will try to start up and then lock out.
Two nights ago it locked out so I tested all 3 range burners at the same time and they seemed to be getting good gas flow.

I took the cover off and checked for anything out of the ordinary but it's remarkably clean in there. The sail switch seems fine and nothing is obstructing it, the connections I can see all look good, the fan seems to spin fine manually.

I've read a bunch on the topic but am having a hard time narrowing it down. All of the RV repair shops around are booked up for weeks so it's becoming a real "situation" as the temperature won't be as forgiving in the coming weeks.

Anyone have this exact situation and a possible fix?

[BFlinn181]

The fact that it shuts down points to a malfunction in the ignition & sensor area. If it tries to start and detects failure 3 times, it shuts down until reset. If it's an older model, it might be a failing thermocouple. If newer, with electronic ignition, there's no thermocouple but the electrodes that spark also sense when flame is present by completing a circuit that is detected by the control board because the flame conducts electricity across the electrodes. Make sure the flame envelopes the electrodes and perhaps try wiping them with a tissue or paper towel. You may just need to replace the electrode unit or clean the contacts between them and the control board.

[USMCRET]

I cannot help you with your specific problem, but since you are willing to take it to a shop, see if you can find a mobile tech service. Those guys can normally get to you much quicker than a RV repair shop.

[Betr2Trvl]

Had a propane flow problem on our new coach last year when we saw sub 30s.

Long story short, new propane valve, regulator, and sail switch did not solve the problem (at least by themselves), but a methanol injection on our propane tank did (the methanol removes moisture in the propane tank that freeze up the regulator when it is flowing enough for the furnace), at least after the other items were addressed. See if you can find a propane supplier that will do a methanol injection for you, as it may be a simple, quick, and cheap magic cure....

And yes I had some propane flow to the stove, at least enough to get it to light. So that is not necessarily a good reference based the flow required for the furnace.

Another potential quick temporary fix, that may well point to moisture in your propane and a freezing regulator, is to hang an old fashioned shop light with a "real" (not LED) light bulb near the regulator to keep the temp above frezzing. However, it's not necessarily the safest thing to do (and certainly not a permanent fix) for obvious reasons......

Good luck!

[EricSirianni]

Man you guys are quick! Thanks so much for the input. I should mention I replaced the regulator already. It looked like the original so it was certainly a good place to start. I also wanted the auto switch for an external tank.

I'll try to determine the age of the furnace and check into the thermocouple or electrode unit.

Good suggestion on the mobile tech. I'll look into it!

I'm going to call around about getting a methanol injection. I do have a feeling it's on the propane side of things. There is a low spot in the piping to the furnace which isn't the case for the other propane appliances which could explain why it's the only appliance having issues. I have a buddy that will hopefully be checking out the propane side of things this week.

[drdarrin]

Originally Posted by BFlinn181

The fact that it shuts down points to a malfunction in the ignition & sensor area. If it tries to start and detects failure 3 times, it shuts down until reset. If it's an older model, it might be a failing thermocouple. If newer, with electronic ignition, there's no thermocouple but the electrodes that spark also sense when flame is present by completing a circuit that is detected by the control board because the flame conducts electricity across the electrodes. Make sure the flame envelopes the electrodes and perhaps try wiping them with a tissue or paper towel. You may just need to replace the electrode unit or clean the contacts between them and the control board.

I had a similar problem on my home unit (NG) and ended up using a piece of crocus cloth on the thermocouple to get it working again. Go lightly. You want to clean it, not alter it.

[mel s]

Originally Posted by EricSirianni

My wife and I are living in our motorhome in the Philadelphia area and it's starting to get below freezing at night. The furnace(Suburban SF-24) works great all day but during the 3 coldest nights in the high 20's it has shut off while we were sleeping. When we finally wake up from the quickly dropping temperature, I switch the thermostat off and on and it normally starts back up but has a high pitched whine for the 15 seconds to a minute. I've never once heard that sound during the day.
A couple times throughout the night it will try to start up and then lock out.
Two nights ago it locked out so I tested all 3 range burners at the same time and they seemed to be getting good gas flow.
I took the cover off and checked for anything out of the ordinary but it's remarkably clean in there. The sail switch seems fine and nothing is obstructing it, the connections I can see all look good, the fan seems to spin fine manually.
I've read a bunch on the topic but am having a hard time narrowing it down. All of the RV repair shops around are booked up for weeks so it's becoming a real "situation" as the temperature won't be as forgiving in the coming weeks.
Anyone have this exact situation and a possible fix?

EricSirianni
When I had a very similar problem with my Suberban SF-42F furnace, (but no high pitched whine), the fix was a replacement ignitor board.
Many RV parts stores have board testers... and some test boards at no charge.
(I suggest you take your board out and have it tested).

BTW this is the board my SF-42F uses: Universal Replacement Ignitor Board Small 4-1/4L x 3-1/4W - $72.9..

Good luck.

Mel
'96 Safari

[EricSirianni]

I was considering the light bulb trick as that's what I have keeping the water compartment warm with It's warmer down there than in the RV sometimes! A light bulb is certainly a safer trick than a torch!

I'll try that tonight! Would the freezing generally happen at the regulator?

[Betr2Trvl]

Originally Posted by EricSirianni

I was considering the light bulb trick as that's what I have keeping the water compartment warm with It'sbb warmer down there than in the RV sometimes! A light bulb is certainly a safer trick than a torch!

I'll try that tonight! Would the freezing generally happen at the regulator?

Yes, the moisture freezes in the regulator. Please reach out to propane suppliers to see if you can get a methanol injection asap though. Probably have to drive to thier location...... As I noted, the light bulb is not a particularly safe solution. In any case, put the bulb above, and not directly on or below the regulator as propane is heavier than air. Obviously, ensure that you have no propane leakage to start with....... Blowing up is not better than being cold......

[Woodlandhill]

What about going down to the store and getting a small electric heat pad? The type used on a sore back or knee...... There should be no spark source if you run the plug out of the compartment and you can put the heat directly where you need it: around the suspect regulator or the low point in the line.

[Old-Biscuit]

High pitched whine when restarting (at night).........
Only moving part in furnace that can make that kind of noise it the FAN blower wheels making contact with cage or MOTOR bearings

Furnace doesn't refire at night (cold) could be spark electrode position/gap
Spark electrode & sensing MUST be centered over burner slot, clean (no soot/carbon) and have a 1/8" gap

And one common issue......DC Voltage.
Have you checked DC System Voltage?

Connections/contacts MUST be clean/tight and good grounds.
Does NOT take much corrosion/dirty contacts/poor connections to STOP 12V DC. It doesn't do well with resistance.

[powderman]

Originally Posted by Old-Biscuit

High pitched whine when restarting (at night).........
Only moving part in furnace that can make that kind of noise it the FAN blower wheels making contact with cage or MOTOR bearings

Furnace doesn't refire at night (cold) could be spark electrode position/gap
Spark electrode & sensing MUST be centered over burner slot, clean (no soot/carbon) and have a 1/8" gap

And one common issue......DC Voltage.
Have you checked DC System Voltage?

Connections/contacts MUST be tclean/tight and good grounds.
Does NOT take much corrosion/dirty contacts/poor connections to STOP 12V DC. It doesn't do well with resistance.

That's a good thought. Because he gets good flame on the stove indicates its not a fuel flow problem. Because it whines, I would say a likely cause is the bearing on the fan is not allowing it to spin fast enough to operate the sail switch.

[Betr2Trvl]

The fact that the furnace works fine above the low 30s points to a propane flow problem to me. The regulator may not be completely frozen, but it is frozen enough to not provide the flow required to light or maintain the furnace flame. While at the same time, it's enough flow to allow the stove to light, maybe even all burners.

I get the consideration about a heating pad, but concerned about wrapping directly around the regulator, particualy blocking the vent (of course venting and any leaks is the safety concern with the light bulb solution).

Maybe an old fashioned hot water bottle with a good fleece cover filled with some really hot water, resting, but not wrapped around the regulator would work too.

The potential easiest and quickest, certainly cheapest, and even more important, eliminating any RV service solution is to just get to a propane dealer and have a methanol injection. It will either work, or not work with immediate results one way or the other.

[ransil]

I had a similar issue. Under 60 degrees it would no light and lock out. Ended up being the ignitor.
I was able to get it to light by blocking the exhaust with my hand while it was trying to ignite, remove hand as soon as it fires.