Furnace problem

[harry t]

'02 Suncruiser 35U furnace fan comes on, burner ignites, moderate heat comes out for 3-5 minutes, then furnace shuts down--long before reaching desired temperature.

Heat doesn't seem as hot as it used to be, and air flow may not be as strong as it once was, or I may be imagining this.

From outside, exhaust air seems to be as hot as always.

Air flows from all ducts, other gas items work fine, thermo clicks in OK, heat pumps OK, etc.

We did hear a louder than usual 'pop' a time or two when the furnace kicked on. Ordinarily, I would have thought that to be ignition, but as I recall, the 'pop' may have sounded about the time the fan should have been activating, and I don't recall ignition being very audible.

Thanks for any ideas.

Harry Thetford
traveling lower AL

[harry t]

'02 Suncruiser 35U furnace fan comes on, burner ignites, moderate heat comes out for 3-5 minutes, then furnace shuts down--long before reaching desired temperature.

Heat doesn't seem as hot as it used to be, and air flow may not be as strong as it once was, or I may be imagining this.

From outside, exhaust air seems to be as hot as always.

Air flows from all ducts, other gas items work fine, thermo clicks in OK, heat pumps OK, etc.

We did hear a louder than usual 'pop' a time or two when the furnace kicked on. Ordinarily, I would have thought that to be ignition, but as I recall, the 'pop' may have sounded about the time the fan should have been activating, and I don't recall ignition being very audible.

Thanks for any ideas.

Harry Thetford
traveling lower AL

[John_Canfield]

Perhaps it is an overheat sensor shutting the system down? If you don't have good airflow, the burner will get too hot setting up a very dangerous situation.

Maybe the blower isn't putting out enough air?

[DerekJ]

It definatley sounds to me like there is not enough air flowing through the system which is causing the furnace to overheat and shut down. This could be caused by a bad fan/blower, clogged filter, or some other airflow restriction. Good luck tracking it down.

[Moder2]

Harry, I just had this same problem.

Either your high limit switch is going bad, or you don't have enough airflow which is tripping the high limit switch.

Check all your vents, make sure they are unobstructed. You also want to check the combustion chamber and make sure you don't have an obstruction there either.

The next place to check would be the fan speed itself, your blower might not be moving enough air.

In my case, we spent a lot of time, and everyone was certain it was an obstructed vent, even suburban. I checked all the vent work with a flashlight and mirror, measured the surface area of all the vents which greatly exceeded the Mfg recommendations, and Suburban still insisted that was the problem. I didn't believe this since it was a new symptom. We tried 3 different high limit switches, and each time it ran fine on the bench, but once it was back in the coach it would overheat and trip the switch. The 4th switch we tried was the ticket, and has since worked fine. I found it really strange we got 3 bad switches, all suburban parts, and the 4th, an after market part worked.

John

[GaryKD]

Hi Harry,
Check the level of propane in your tank. I have had the sympton you describe. After much frustration and activity like previously posted, I filled the propane tank. All worked fine. When my tank reads 1/4 it must be less than that. I do not remeber how much it took to fill the tank. All other appliances workd throughout this adventure. All I can figure is the furnace takes a lot of propane and when the tank gets to 1/4 there is not tnough pressure to supply what is needed.

The bottom line is I know to keep the tank full and the furnace will work fine.

[harry t]

Hello, guys, and thanks very much for your responses. This morning I took the cover off and everything looked clear from there. I have screens over the vents. Also checked one floor register that had a few particles of dust and lint.

Tonight we fired the furnace up to see if we had the same symptoms before replying back to your suggestions.

I should not have been surprised that it seems to be working normally, inasmuch as it is in the 40s tonight and I can use heat pumps.

We definitely have more air flow tonight, much more heat, and it kicked off at the desired temperature.

The problem may reoccur and one or more of your suggestions will probably end up being the culprit.

But for the time being, I have ONE CONCERN/QUESTION, seeing as how some of you mentioned the danger of overheating/undercirculating.

Tonight I went outside the coach during the furnace operation. The heat coming from the furnace seemed awfully hot. It was uncomfortable when holding my bare hand 10-12 inches from the exhaust. How does this compare with other furnaces?

John, Derek, Moder2 and GaryKD, Thanks again for your responses.

Harry T.

[FleetMan]

Harry,
The propane furnace in an RV is extremely inefficient. All that waste heat you felt is normal, thus the warning posted by the exhaust vent. Sure would be nice to be able to capture that heat and route it back inside.

[RV Wizard]

Harry, when you were having problems with the furnace were you operating off shore power or generator?

[FrontRangeRVer]

Harry, make sure ALL your inside registers are open...your heat switch might have operated and shut off the gas to the unit.

And yes....you will burn your hand if you hold it too close to the flame output outside when your furnace is running....this is normal.

[Izzyblueye]

FLEETMAN: You are absolutely right about the wasted high degree heat out of the furnace. I am certain there is a way to put this loss to work through a second exchanger of some kind. I wish I was an engineer. We seem to accept waste so readily in this country.

[harry t]

Thanks again for your suggestions.

Mike and Amy--I am operating from shore power.

As for the propane quantity suggestion earlier--I show one third on the inside panel, but just over one half out on the propane tank itself.

I am happy to hear everyone's exhaust heat seems to be about as hot as mine, even though it's a shame to waste a precious commodity.

Someone mentioned checking my furnace filter--At the risk of a dumb question, where might that be?

Harry T

[Pusherman]

Harry, I don't believe you have a furnace filter. I don't know of any Winnies that do.

There is a filter for the a/c / heat pump, though. Located next to the head of the bed over the basement air. Slightly different locations in different Winnies, but generally in the same location. Be sure to change this filter frequently or it will impact your air conditioning (and heat pump) functioning.

[M&EM]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by harry t:
Thanks again for your suggestions.

Mike and Amy--I am operating from shore power.


Harry T </div></BLOCKQUOTE>

Harry check your DC voltage. Even tho your on shore power, It is possible to have lower then normal converter voltage if it is similar to the ferro resonant converter I recently had go bad. Lower voltage will manifest itself with lower air mover volume as well as causing the furnace gas valve to turn off sooner at some preset low battery value. I don't recall that value, but it is associated with a discharged battery voltage level.

Marty