Furnace

[Spencer]

I have furnace that is and has been hooked up to gas, but hasn't been run in a long time, I tried to fire it up. The furnace only blows cold air,.. I know the valve is on, but no heat. Is this a simple fix or is it major?

[Bob Miller]

I have found that furnaces that haven't been used in a while get a bit cranky and may require as many as 10 cycles of the start-up sequence to get going. This is to get things un-stuck (see below) as well as get LP gas down the lines to the solenoid. After it doesn't start, turn it OFF for 1-2 minutes and try again.

The second most common cause of long dormant furnaces not starting is a stuck sail switch. This is a switch that must sense the airflow at a certain volume before it will let the gas solenoid open. Some are easy to reach, some not so easy. If you are trying to start with just battery power, try plugging in the shore line for a bit more DC Voltage/current, that sometimes doe the trick, but the sail switch is usually the culprit. On some furnaces you can poke the sail switch with a long wire and get it unstuck, on others it requires taking everything apart.

[Carol H]

Sometimes if they have not been used for a long time - something as simple as a spider web will stop it from lighting up..... so it needs to be cleaned out.

Which furnace do you have? You may find the manual for it in the Document center here - which should have instructions for cleaning it.

[Donna D.]

If my rememberer is working correctly, Spener your trailer has a Suburban furnace. Carol is right, check the Document Center for a manual that may help: Fiberglass RV - Document Center - Furnaces/Heaters

[Bob Miller]

Carol's post jogged my memory. We don't see them in SoCal very much, but I have heard about "Mud Daubers" building nests in the furnaces outside intake and exhaust ports, cutting off airflow to the combustion chamber/sail switch.

[Dan Meyer]

I'd bet the issue is simply air in the gas line. Start the furnace for 2-3 minutes, and shut it off for a few minutes, and try again. It might take 8-10 times or more to purge all the air before the furnace works properly.

-- Dan Meyer

[Daniel A.]

I always light the stove burner before trying the furnace to take care of air in the line.

[Spencer]

Thanks to all for all the help, I have been quite busy lately, and haven't had time to look at it,.. I don't know the brand of it, it is a long square, tin box that that fits right into a square opening. I haven't tried all the suggestions, but I have lit the stove top burners for a while before trying to light it.

Someone said something about a pilot-light.. IS that something that I have to manually light..? I have no manuals.. Hopefully this next week I will have more time to monkey around with it.

[Daniel A.]

Depends on what unit you have some have a pilot light and others are electronic.
If the unit is electronic one thing to know is that part of the start procedure is for the fan to come on and sweep for a few minutes before firing.

[john warren]

this could be really simple,,, or only sorta simple.
first things first, i take it you don't know if it has an igniter , or a pilot light. thats the first thing to find out,,,maybe you have to light the pilot.

then does it match light ? or have a lighter lever that you flip to light it?

and finaly is it auto ignite?

and finaly finaly,,if it has a pilot that won't stay lit,,, replace the thermocoupler.

then take two asprin,,,lay down, and call me in the morning!

[Bob Miller]

If you don't have a manual for the furnace it is a good idea to find the I.D. plate and then google the make and model # followed by "manual". About 98% of the time you will come up with installation and operating instructions.
I do this for all of the appliances and systems in RV's I restore and always wind up with a nice thick documentation package to pass on to the next owner.

[rabbit]

Mud dauber wasps will do the same for your water heater air outlet baffles. Usually dries and shakes down into the outer cmptmt. while towing. Outside air entry into non-pilot furnaces is limited by comparison but a wasp and certainly a spider can go just about anywhere and course mesh or screen wire is no impediment to a spider.

jack

[Spencer]

IT WORKS..!!

Thanks to everyone who posted suggestions. All I really tried was what Bob Miller said about cycling it out about 10 times.. I also poked the flag switch with a stick. I have heard reports about these furnaces making a crackling sound when heating up, and cooling back down which awakens the occupants, but this works quietly, and just as it is suppose to.
I only spent a little time with this, and zero dollars.

Again..
MANY THANKS

[Donna D.]

Originally Posted by Spencer

IT WORKS..!!

I only spent a little time with this, and zero dollars.

Again..
MANY THANKS

I love it when a plan comes together

[Carol H]

Thanks Spencer for sharing with us what worked. I often look at problem posts and wonder what suggestion ended up working.

Enjoy your furnace!