Furnace blowing but no heat

[pegski]

Okay I solved most of my electrical problems for the lights and heater so took off again on a long camp trip. Turned on the furnace tonight but it’s only blowing cool air. Not cold but not hot no matter how high I have it set and the thermostat is wonky as it turns off often. I’ve looked and don’t see a flame. What should I check? Battery is fully charged.
Thanks in advance.

[Steve Outlaw]

Sounds like your sail switch is sticking. Bang on the side of the furnace right after the fan starts blowing. That usually unsticks it.

[gordon2]

Assuming you have propane and the regulator is working...

See page 27 of this guide.

[Wayne Collins]

It has to go through a purge cycle to clear any unburnt gas, first, then tries to ignite the gas
If it is not getting LP gas it will shut off.
Older units might be harboring spider nests or something else.

We carry a small electric heater, which is much quieter,

[Bing M.]

Be aware there are two models of sail switches. There is a single try which shuts down after one try to open the gas valve. You then have to turn down the thermostat and then turn it back up. The other model is a three try which will try to run after a short period, allowing any gas to clear, and then retry for a total of three times. As Steve Outlaw says the sail switch can sometimes stick and a good bang on the side may free it. If this is the problem, get it checked out even if the banging gets it going. It could lead to a safety problem and it is a simple replacement to do.

[Gerry]

I assume it is electronic start.. Raise thermostat and listen close near the furnace. After blower starts there should be a slow down in the motor of the blower, when the GAS VALVE tries to turn on and then you should hear a series of clicks and if you look in the sight glass, you may be able to see the ignitor sparking to light gas.

[Jann Todd]

Originally Posted by pegski

Okay I solved most of my electrical problems for the lights and heater so took off again on a long camp trip. Turned on the furnace tonight but it’s only blowing cool air. Not cold but not hot no matter how high I have it set and the thermostat is wonky as it turns off often. I’ve looked and don’t see a flame. What should I check? Battery is fully charged.
Thanks in advance.

Our furnace starts blowing cold air as soon as the blower comes on then in a couple of minutes the furnace lights. This is a safety item to make sure there is not a build up of propane in the furnace that could cause an explosion. Are you waiting long enough for the heat to actually come on?

[pegski]

I was waiting quite a while but the odd part was the air was cool, not cold, but not warm. I took someone’s advice and gave it a couple of whacks and that must have done it because it’s working again. Thanks for all the replies.

[dmad1]

The fan coming on before ignition may have saved us in a way. One morning in NM, when I turned on the furnace, we got a strong dose of propane. Found a mobil mechanic to come out and when the unit was taken out, the inlet propane line had a loose connection. So glad it was made to clear out the vents before it lights.

[Jann Todd]

Originally Posted by dmad1

The fan coming on before ignition may have saved us in a way. One morning in NM, when I turned on the furnace, we got a strong dose of propane. Found a mobil mechanic to come out and when the unit was taken out, the inlet propane line had a loose connection. So glad it was made to clear out the vents before it lights.

That's why there are those safety items built into the furnace. Just in case of a propane build up from any cause. Glad you smelled it and got it fixed or you might have exploded.

[gordon2]

Originally Posted by dmad1

The fan coming on before ignition may have saved us in a way. One morning in NM, when I turned on the furnace, we got a strong dose of propane. Found a mobil mechanic to come out and when the unit was taken out, the inlet propane line had a loose connection. So glad it was made to clear out the vents before it lights.

Sounds like the gas was leaking so if the concentration became sufficient then any ignition source could have set it off, even if the furnace was not being used. That is basically what happened in a Scamp about a year ago, injuring two.

It also seems like there has been a rash of these events at home lately, including a home exploding only a few miles from me that killed a woman a few months ago and the one in Maine this week that killed a firefighter and injured six others.

Hopefully these cases will convince everyone who uses propane to use a propane detector / alarm and to get inspections and tests of their RV propane system using a manometer annually or as needed (because of changes in the system, suspected damage, etc). Its also a good idea to turn the valve off at the tank when the propane is not being used for a while. And remember that propane regulators dont last forever, and if it is not mounted properly it could fail much sooner. That is what happened to mine, resulting is propane escaping (fortunately outside the camper).

[dmad1]

We were very lucky that we had not left the furnace on during the night. I guess we caught it before the detectors did because they did not go off. The mechanic felt like the fitting had not been tightened at the factory since the trailer was only a few months old. It was the first trip to the mountains, so we had not used the furnace until then but we had used propane for cooking and hot water, etc.
A few years ago at Quartzsite, AZ. A group of 5 trailers in sort of a circle were camped nearby. A group loaded up and went shopping. About 30 minutes later, their trailer exploded. Didn't completely destroy it, but blew out the windows, etc. and pushed out the walls but remained intact. Luckily, there was not a fire. Only a lot of damage.