View Full Version : How to bleed a propane furnace after tank runs empty

Mar 15, 2008, 02:38 PM
I believe I need to bleed the propane line to my furnace. The propane tank ran empty and the furnace lit only briefly right after the tank was refilled. (It's possible that the propane tech and I were both mistaken and we just heard the fan and not the burner.)

But I can't find where to bleed the line. It's far more complicated than a water heater. I have the main valve in the 3/4" line into the unit. There is the on/off valve inside. And that's all I can find. There are a couple of places inside where it looks like I could open one of the copper lines, there are capped T-joints with removable caps, but they aren't at the top which is where I would expect to bleed from (since propane is heavier than air).

The restart instructions say to turn off the thermostat, the main power to the unit, the gas supply line and the on/off valve inside, wait 5 minutes, turn on the on/off valve, put the covers back on, turn on the gas supply and the power, then turn on the thermostat. I've been through that cycle about a dozen times. The fan comes on and I hear the clicking of the ignition spark, 3 or 4 times a second for about a minute. Then it all shuts off. Sometimes the fan and the spark start up again right away, still with no ignition, sometimes it sits and I can get it to start trying again by throwing the power off and on again.

I get a very faint hint of propane smell which I think is coming from the gas that is not being ignited by the spark. If I have gas and spark, I should get ignition, unless the gas has air in it and is not concentrated enough to light. Which is why, combined with the tank running empty, makes me think I need to bleed the line.

But so far my only method for bleeding is to get a little bit more out each time I go through the shut-down, wait, try-again cycle. There has to be a better way.

Any suggestions for how to find where to bleed the propane lines?


Mar 15, 2008, 03:16 PM
It's fixed. I think I have a clue what fixed it.

If the slight hint of gas that I've been smelling is the gas/air mix that I'm trying to bleed out, and if it's coming out when the burner tries to light from the electric spark, then I figured that the more I heard that sparker going, the more I was bleeding the line.

So, instead of following the safety instructions of waiting 5 minutes each time I tried, I decided to see what would happen if I just kept trying. The circuit breaker for the furnace is close enough that I can hear the sparker, so when the unit quit trying to light itself, I just turned off the circuit breaker and turned it back on again. The unit immediately tried to light again and I could hear the sparker snapping for about a minute. It shut off again so I flipped the breaker off and on again. I kept this up for about 10 or 12 tries and suddenly the burner lit!

My current theory about what made it work is that it was a combination of the dozen or so times I tried the shut-off/wait/turn-on cycle plus the dozen times in a row that I tried it this final time. Each time it bled out a little bit of the air in the line that I needed to get rid of. Finally, after enough little dribbles of bleeding, there was enough propane in the mix for it to light.

If I'm wrong, and especially if there's something wrong with the way I'm thinking about it as to be really dangerous, I'd really appreciate one of the experts letting me know. For now I'm grateful that my furnace is working again.


Eric D
Mar 15, 2008, 03:54 PM
It's fixed. If I'm wrong, and especially if there's something wrong with the way I'm thinking about it as to be really dangerous, I'd really appreciate one of the experts letting me know. For now I'm grateful that my furnace is working again.


First off I'm glad you got your furnace back running. However... (you had to know this was coming) :rolleyes:... there are always dangers to do something other then what the manufacturer recommends. The relighting of the furnace and the water heater pilot, or any other device with a pilot, is the responsibility of the propane service tech. Did the technician purge your tank after running it empty? He should have. Running a tank empty presents that possibility of air getting into it. This is why new tanks or tanks that have been allowed to go empty have to be purged. The right course for you should have been to call the propane company back.

I'm happy everything worked out for you.:)


Eric D

Feb 3, 2011, 12:56 PM
Mine ran out of propane too. I have been trying to relit it for two days. My tanks are the kind that you take in and get refilled. I live in a small RV trailer. I didn't relize it was low until I smelled a odd odor ( not rotten eggs ) like gas fumes. I turned off the empty tank and opened the new tank. I think the line may be frozen somehow... I know the dealership wasn't any help. Roads too bad to get out and no other recourse than an electric heater. I am hoping when it gets above freezing, that it will light. Cox_dianne@yahoo