Furnace Problem

[Big-B]

Greetings,

We are having an intermittent problem with our furnace on our 3055 Big Horn. After having a mobile tech come out to troubleshoot it when it was completely dead the tech replaced the thermostat and everything seemed good. Fast forward a few weeks and we were packing things for the winter trip. I left the furnace on and set it to about 50 overnight. Next morning I went out and checked it and it was 25 degrees inside.

I called the mobile tech and he came out and looked at it again. Sometimes it would work OK and other times it would fire up 3 times and then need to have the thermostat turned off and back on to reset the furnace. When it starts it usually has a fairly loud howl until it starts and keeps going. The tech pulled the furnace (a suburban 35k btu unit) and took it back to his shop to bench test it. He said it worked fine on the bench and he couldn't find anything wrong with it.

He re-installed the furnace and I told him I would leave it on overnight as we were planning on leaving the next morning. When I checked it then next morning the trailer was 30 degrees inside so I called the tech again. He came over and called suburban tech support and they had no idea what was wrong either.

It lights every time and I can feel heat coming out of the exhaust but if it howls it won't stay lit. If it lights and howls and the howl goes away it will stay running until the thermostat tells it to turn off. In the week and a half that we have been gone it has only failed to stay running one time but it is annoying to not have it work properly.

It does the same thing as a residential furnace does when the flame sensor gets dirty but the tech told me everything looks good. In fact the furnace looked like it had never been run at all. It is a 2010 Big Horn.

Does anybody have any ideas what could be going on with this furnace?

Thanks,
Brian

 

[danemayer]

Hi Brian,

Screeching or howling can be a symptom of too much primary air - a bad mix of propane and air. You may have a problem with poor propane flow to the furnace. This could be a regulator/pigtail problem, or less likely, a buildup of oil in the propane hose coming out of the dual regulator, as it loops down and back up to attach to the iron pipe.

That would fit with the finding that everything works ok on a bench test of the unit. When the furnace attempts ignition, there's a flame sensor that determines if it was successful. After 3 failures, for safety reasons, the unit is designed to lock until the thermostat is recycled. Poor propane flow could also cause that. I think there's a propane pressure test port on the furnace where a technician can use a manometer to test for 11" Water Column Pressure. If not, the propane pressure can be tested at the cooktop.

Also make sure you don't have anything restricting airflow of vents, or of the main air return to the furnace. Either could affect normal operation.

 

[myla296]

Not a fix for your furnace so ignore this if you are really wanting it to work. But, I circumvented my furnace problems (after having trouble with it running and seeing how inefficient they are anyway) by using space heaters on power strips with breaker switches.

(My furnace problem may have had to do with the metal sensor on the back being sensitive and shutting off the heater before the thermostat was up to temperature, and the air heating is very inefficient. It gets heated in the box and the fan tries to blow it generally toward this one circle on the back --that goes to the ductwork-- but it just seemed like a really lousy way to run heat, hoping enough of it randomly finds its way toward that one opening...the fan was not placed there to help facilitate this so...went with space heaters). **I did resort to this after consulting my RV community that I used to live among, with many long timers who always knew more than me.**

 

[Big-B]

Thanks for the reply Dan.

The mobile tech did suspect a bad regulator and checked the gas flow by running all 3 burners on the stove when the furnace was running as well as fridge and water heater. The flame on the stove didn't change as he added usage.

A friend of mine was telling me about having similar problems with a furnace in his pickup camper years ago. An old rv repair guy found a ceramic piece in the igniter or flame sensor had a micro crack in it and he said it worked OK when it was cold but when it warmed up the crack opened up and caused problems.

We have been on the road for 10 days and it has only let us down one night but I like things to work right every time. This is our 4th fifth wheel and this is the first furnace problem we have ever had.

There have been a couple of other odd problems but I will start separate threads for them.

- - - Updated - - -

Myla,

Thanks for the reply. We do have 2 electric space heaters and they are both running as I speak. We are in a campground for a while in New Mexico but sometimes we stay in Walmart parking lots when we are just putting miles behind us and don't need any of the services that campgrounds offer.

The only generator we have is a Honda 2,000 watt inverter generator so we can only run one heater at a time but it does make it a lot faster to heat the place up when we can run a electric heater and the furnace at the same time. It comes in real handy when we stop to camp and the camper is 20 degrees inside.