FIXED: Furnace shuts off after 30 seconds

[JohnD]

Have had this conversation going in another topic, but thought I'd start this in it's own thread.

Two weeks ago while camping the furnace was running and the LP tank ran out of gas.

I shut the furnace off as it was warm in the trailer and went outside and flipped the switch on the regulator to the other tank.

An hour or so later I turned the furnace back on as it was getting a little chilly inside and the fan ran for about 30 seconds . . . then shut off.

No heat.

I waited a few minutes and tried it again . . . same thing . . . a couple more times . . . same thing.

The stove and refrigerator runs fine, as does the water heater, although the water heater doesn't sound like it is burning as strong as it was before!

Tried the furnace again when we got home . . . same thing . . . and then again this morning . . . same thing.

I swapped the 2nd. tank to the other side of the compartment (where the first tank was) and tried the furnace . . . 30 seconds and off!

So . . . I took the empty tank up this afternoon and had it filled and put back where it was originally . . . 30 seconds and off!

All of the other stuff that runs on propane seems to work (except the water heater still doesn't sound the same as it did before).

The interesting thing about this is that the only thing I did was to flip the switch on the tank regulator and nothing else . . . and then this problem started.

Ironically, we've had our Prowler for 15 months and that first tank lasted this long (including a two week winter trip to Tucson last February - nine campouts total)!

I'm thinking that maybe the switch is broken (or something) on the tank regulator . . .

Or could it be something else?

 

[MTPockets]

Re: Furnace shuts off after 30 seconds . . .

John, it doesn't sound like the regulator if other appliances work. Your furnace should have a two year warranty. If you don't figure it out, call the furnace mfg; maybe they can guide you.

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

John, it doesn't sound like the regulator if other appliances work. Your furnace should have a two year warranty. If you don't figure it out, call the furnace mfg; maybe they can guide you.

Could it be the thermocoupler (or whatever that is called)?

 

[wdk450]

Re: Furnace shuts off after 30 seconds . . .

Had another forum report strange heater malfunctions, and it was the sail (airflow detection) switch malfunctioning, shutting down the furnace. This has been reported on this forum, too.

 

[Bogie]

Re: Furnace shuts off after 30 seconds . . .

John,

You don't say which heater you have. I have a Suburban SF 25F. They aren't terribly complicated, but it helps to have documentation. Here is a link to the Suburban service manual. If you have one of these, check out pages 26 (Sequence of Operation) and page 29 (Service hints and diagnosis). This may help you diagnose what's going on.

You said the heater runs for 30 seconds and stops. Is the fan just running? In the Suburban, the fan needs to start and operate the sail switch in order for the circuit board to start the spark electrode and start the gas flowing. If the sail switch doesn't operate properly, it won't turn on the gas.

I keep an extra sail switch and a spare circuit board in my repair kit.

I hope this helps.

 

[dlw930]

Re: Furnace shuts off after 30 seconds . . .

John, before you start buying parts, you might check for loose or corroded electrical connections on or to the circuit board. It only takes a small, almost imperceptible, amount of corrosion to keep a 12v circuit from being completed. Since the fan is apparently coming on, the circuit board is being powered, but could be something loose elsewhere.


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[JohnD]

Re: Furnace shuts off after 30 seconds . . .

It is a Suburban (not sure of the model #) . . . and it is just the fan that runs for 30 seconds.

 

[codycarver]

Re: Furnace shuts off after 30 seconds . . .

So, The fans cycles. Does the burner fire during the cycle?

If it doesn't I'm going with a loose connection or the sail switch. I'd pull the outside cover off and try moving the wires while the fan is cycling and see if it fires. Next the switch.

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

So, The fans cycles. Does the burner fire during the cycle?

If it doesn't I'm going with a loose connection or the sail switch. I'd pull the outside cover off and try moving the wires while the fan is cycling and see if it fires. Next the switch.

Didn't hear the burner try to fire . . .

 

[LBR]

Re: Furnace shuts off after 30 seconds . . .

Had you checked for blockage of sort in the intake/exhaust that would slow airflow so much that the sail couldn't activate it's switch?

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

Had you checked for blockage of sort in the intake/exhaust that would slow airflow so much that the sail couldn't activate it's switch?

I've looked in there with a flashlight . . . didn't see any blockage.

Plus, we had been using it (furnace) for three nights straight before this happened without any problems.

The problem started when I switched the regulator over to the second propane tank after the first one ran out of gas.

 

[wdk450]

Re: Furnace shuts off after 30 seconds . . .

I've looked in there with a flashlight . . . didn't see any blockage.

Plus, we had been using it (furnace) for three nights straight before this happened without any problems.

The problem started when I switched the regulator over to the second propane tank after the first one ran out of gas.

Sometimes concurrent problems happen. Maybe something else decided to quit at the time the tanks were switched.

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

Sometimes concurrent problems happen. Maybe something else decided to quit at the time the tanks were switched.

I'm going to call Suburban in the morning to see what they say . . .

 

[danemayer]

Re: Furnace shuts off after 30 seconds . . .

Make sure you don't have any vents or the air return blocked. Reduced airflow can prevent the blower from getting up to speed, which keeps the sail switch from operating, which prevents the igniter from getting voltage.

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

Make sure you don't have any vents or the air return blocked. Reduced airflow can prevent the blower from getting up to speed, which keeps the sail switch from operating, which prevents the igniter from getting voltage.

Interesting that you mention that . . .

I did have the basement wall out the afternoon before retracing the coax as the cable connections were acting up again, and the furnace hose to the bedroom kind of droops over the wall and looked like it was half blocked off.

I remember that I had to fuss with it to get it into position when I put the wall back in.

I may have to do something different with the way that furnace hose runs over the basement wall.

I'll go out in a few minutes and check that and give the furnace another try!

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

Make sure you don't have any vents or the air return blocked. Reduced airflow can prevent the blower from getting up to speed, which keeps the sail switch from operating, which prevents the igniter from getting voltage.

Interesting that you mention that . . .

I did have the basement wall out the afternoon before retracing the coax as the cable connections were acting up again, and the furnace hose to the bedroom kind of droops over the wall and looked like it was half blocked off.

I remember that I had to fuss with it to get it into position when I put the wall back in.

I may have to do something different with the way that furnace hose runs over the basement wall.

I'll go out in a few minutes and check that and give the furnace another try!

Just tried the air flow test . . . fan still runs for 30 seconds then shuts off.

 

[JohnD]

Re: Furnace shuts off after 30 seconds . . .

Well . . . just got off of the phone with Suburban Customer Service . . . wait a minute, what customer service?

They have no technical support and all they would do was tell me (several times) to call my dealer and make an appointment.

Anyway, I've got the inside and outside covers off of the furnace . . . it is a Suburban SFV-35Q.

Before I took the covers off, I tried one more thing . . . set the regulator to the middle and opened both tanks and still get the fan for 30 seconds.

I also ran the stove and had fire on all three burners.

Anyway, now I just noticed one other thing . . .

The regulator has that little window that is supposed to turn red with the gas is empty or off . . . and it isn't turning red.

I also disconnected both tanks from the regulator and still the window is not turning red.

I seem to remember that the switch on the regulator had click indents as it was turned from one tank to the middle to the other tank, and now that dial just rotates smoothly.

I'm going to Camping World in about a half hour for some other things and will check one out to see how it operates (plus they are doing free hot dogs and burgers from 11 a.m. to 1 p.m. today).

 

[danemayer]

Re: Furnace shuts off after 30 seconds . . .

If it was poor gas flow, the igniter would fire but the flame sensor would shut things down because the flame wasn't hot enough. It would try to ignite 3 times before locking out and requiring a thermostat reset.

If it never fires the igniter, either power is not getting to the board, or through the sail switch, or to the igniter, or the board is defective. Could also be the igniter, but the board is much more likely.

Unfortunately, while Suburban may cover under warranty, via a dealer or other authorized Surburban servicer, they will probably not send you parts or reimburse parts for self-install.

 

[MTPockets]

Re: Furnace shuts off after 30 seconds . . .

We had a problem a few years ago with the water heater. It cost me $75 for a mobile tech and the parts under warranty, sent to the tech. It may be worth it to go mobile instead of dragging it to a dealer and waiting.

 

[gwalter]

Re: Furnace shuts off after 30 seconds . . .

John, Brian Lajoie can recommend a good Mobil tech for you.