Furnace no gas

[Horsemen]

Hey folks - I see so many furnace troubleshooting threads but could not find this specific issue.

I have a Suburban SF-30F that runs but will not make heat. I bench tested and confirmed the high limit switch is ok, the sail switch is ok, the motor runs, the igniter fires, I can see spark.

I do not smell propane (or very faint) coming out of the exhaust when it attempts to fire up.

I have gas running to the stove no problem.

I am wondering if anyone has experienced issues where the gas pressure is good enough for the stove but too low for the furnace? Maybe the tank is too low to provide adequate pressure for the furnace? Is that possible? Another thought is perhaps the regulator on the tanks are not operating properly and that should be replaced?

I'd like to avoid pulling the unit back out if I can solve it with the above - if not my next steps would be ohm testing the gas valve on the furnace, if that's ok maybe pulling the valve and the burner to check for obstructions but it's a really clean unit and from what I understand that's a lot of work. After that I'm really out of ideas.

Any suggestions would be appreciated.

Thanks!

 

[Henry J Fate]

A better test for gas flow is your hot water. Check to see if that works. If that works, sounds like a gas flow problem at the furnace. I would then suspect either the furnace gas valve or the nozzle.

 

[Gary RV_Wizard]

Standard regulated LP gas pressure is very low anyway, about 0.5 psi. So unlikely that lack of pressure is a problem. Sometimes the furnace or water heater suffers from a lack of gas volume (flow), but that is typically a cold weather problem, where low temperatures slow the rate the gas vaporizes in the tank. That happens whether the tank is full or near empty.

Try the water heater as Henry suggests. If that fires up ok, you have adequate pressure and flow.

The most common cause for your problem is poor intake & exhaust air flow. The burner is very sensitive to air/fuel ratio and any disruption in the combustion air intake or exhaust tubes will prevent ignition. Rust flakes, cobwebs, insect nests, etc. are common culprits. Clean the tubes thoroughly and give it another try.

 

[Horsemen]

A better test for gas flow is your hot water. Check to see if that works. If that works, sounds like a gas flow problem at the furnace. I would then suspect either the furnace gas valve or the nozzle.

Thank you Henry - it's a new for me RV (2005 Keystone sprnter) not hooked up to water yet, in the cold northeast trying to get the kinks out and ready for above freezing temps.

I'll follow your instructions and pull it out again and start with the ohm test on the valve, if that fails to identify the issue I'll disconnect the gas feed tube from the valve and open the hatch to the igniter and venturi and check the nozzle / flow on both ends. I'll keep you posted. Thanks for the help.

 

[Horsemen]

Standard regulated LP gas pressure is very low anyway, about 0.5 psi. So unlikely that lack of pressure is a problem. Sometimes the furnace or water heater suffers from a lack of gas volume (flow), but that is typically a cold weather problem, where low temperatures slow the rate the gas vaporizes in the tank. That happens whether the tank is full or near empty.

Try the water heater as Henry suggests. If that fires up ok, you have adequate pressure and flow.

The most common cause for your problem is poor intake & exhaust air flow. The burner is very sensitive to air/fuel ratio and any disruption in the combustion air intake or exhaust tubes will prevent ignition. Rust flakes, cobwebs, insect nests, etc. are common culprits. Clean the tubes thoroughly and give it another try.

Thanks Gary - that's good info. I'm in the cold NE and the tank seems pretty low - so I'll fill it and try again - cant further will need the gas anyway. I'm not hooked up to water yet so can't do the hot water test.

I will hook a shop vac up to the intake and exhaust ports and give it a good vac out. The unit looked super clean when I pulled it but like you said is sensitive so maybe a little unseen debris deep inside.

I'm sure we'll figure this out..hopefully before I need the AC on lol.

Thank you very much

 

[Rene T]

You can do the hot water test. Just fire it up and immediately turn it off if it works OK. You’re only trying to prove it does start and not heat water.

 

[Matt_C]

Horse,

Did you last buy gas in NY? If not, and you bought it someplace south, you may have not gotten Propane, but LP as a mix of Propane and Butane. You have burned off the Propane and now the butane is sitting quietly in the bottom of the tank waiting for things to warm up.....

After you do the shop vac trick, and it still won't light, Open the stove and pull a burner out. Look and the size of the jet that got exposed when you did that and then go and get a length of clear tubing you can push on there and a pair of rubber bands and a yard stick.

Use the rubber bands to hold the tubing to the yard stick. Put about a foot of water in the tubing. Plug the open end on the burner jet and turn that burner on. There should now be a difference of 11" between the tops of the water in the tube. It should stay that way when you try to fire the heater.

If it does not, you have a gas delivery problem.

Matt

 

[Gary RV_Wizard]

Problems with furnace gas valves are really rare, and general gas delivery problems are almost as rare if the LP system is functioning at all (as witnessed by the stove working ok). If the stove, fridge & water heater light off ok, I wouldn't spend much effort trying to validate gas system flow. Nor do I consider a nose sniff test at the exhuast pipe to be good evidence that the gas valve did or did not open.

 

[Horsemen]

You can do the hot water test. Just fire it up and immediately turn it off if it works OK. You’re only trying to prove it dose start and not heat water.

I didn't know that - thank you Rene. Will be early on my list of next steps, in addition to the vac out.

Thanks!!!!

 

[Horsemen]

Problems with furnace gas valves are really rare, and general gas delivery problems are almost as rare if the LP system is functioning at all (as witnessed by the stove working ok). If the stove, fridge & water heater light off ok, I wouldn't spend much effort trying to validate gas system flow. Nor do I consider a nose sniff test at the exhuast pipe to be good evidence that the gas valve did or did not open.

Okey dokey Gary. After the other systems fire up and the vac out is done, I'll test and update here.

If still no heat maybe pull the furnace back out (would love to avoid this - it's a bit of a pain especially getting back in) quick valve ohm bench test in cycle (assuming that would eliminate the board) then open the case to see I'd the igniter looks good and is positioned properly, and if there is any debris inside the venturi or gas tube leading in from the valve. Hopefully one of these will solve it - I'll update here. Thank you Gary!

 

[Horsemen]

Horse,

Did you last buy gas in NY? If not, and you bought it someplace south, you may have not gotten Propane, but LP as a mix of Propane and Butane. You have burned off the Propane and now the butane is sitting quietly in the bottom of the tank waiting for things to warm up.....

After you do the shop vac trick, and it still won't light, Open the stove and pull a burner out. Look and the size of the jet that got exposed when you did that and then go and get a length of clear tubing you can push on there and a pair of rubber bands and a yard stick.

Use the rubber bands to hold the tubing to the yard stick. Put about a foot of water in the tubing. Plug the open end on the burner jet and turn that burner on. There should now be a difference of 11" between the tops of the water in the tube. It should stay that way when you try to fire the heater.

If it does not, you have a gas delivery problem.

Matt

Thanks Matt - I've got my weekend project list cut out for me. Much appreciated.

 

[Lou Schneider]

Horse,

After you do the shop vac trick, and it still won't light, Open the stove and pull a burner out. Look and the size of the jet that got exposed when you did that and then go and get a length of clear tubing you can push on there and a pair of rubber bands and a yard stick.

Use the rubber bands to hold the tubing to the yard stick. Put about a foot of water in the tubing. Plug the open end on the burner jet and turn that burner on. There should now be a difference of 11" between the tops of the water in the tube. It should stay that way when you try to fire the heater.

If it does not, you have a gas delivery problem.

Matt

Be careful with this - some stoves have a secondary regulator that can skew the results. It's a cube usually right at the gas inlet.

 

[Gary RV_Wizard]

Okey dokey Gary. After the other systems fire up and the vac out is done, I'll test and update here.

Just to be clear, I didn't mean those things are never, ever, a problem. I was just trying to help you prioritize your efforts.

Another hint: If you hear the igniter click, you know the fan is running at the required speed and the sail switch is closed because the igniter cannot function unless those have already worked as designed. No need to test them separately. I explain the sequence of operation in my magazine article on Furnace Troubleshooting. We don't yet have the forum Library up and available with this new software, so I'll attach my article.

 

[Horsemen]

Great news folks - ok, very encouraging.

I vac out the pipes - got a good deal of rust / dirt - maybe 1-2 tablespoons. THANK YOU!

I did the hot water heater test, it fired up no problem - CHECK. THANK YOU!

Ran 'er up - still not firing - pulled 'er out again and set up for more bench testing.

I did the gas valve solenoid ohm test - 37 ohms - CHECK

I bench tested the signal going from the board to the gas valve - CHECK

Tried to see if I could blow air through the gas inlet while bench testing and the board was signaling the gas valve to open. FAIL (like yall were saying - looks like a clog in the tube...)

Opened up the case - saw more debris around the burner...hmm Once again, you experienced folks were leading me down the right path.

Tried to blow air through the tube out the nozzle - FAIL FAIL FAIL nozzle / gas tube was clearly clogged. Tried reverse flowing air away from the nozzle back through the tube (I'm not going to tell you how - let's just say ewwww gross) - BINGO Look at the pics to see what uninvited guests came to the party!!! A bunch of lil buggers in my gas tube clogging up the nozzle.

I'm very optimistic after a thorough cleaning and sewing 'er back up and runnin 'er she'll fire up. Too late for me to complete the job tonight- but I'm delighted to have finally found something significant that will likely resolve the issue.

I'll give you a final update after reinstalling and running her up.

THANK YOU ALL very very much! Very satisfying to make progress with this finally.

 

[Horsemen]

Oh man...I just did my homework and Google lensed these dudes...FLEAS

I bought the RV about a month ago from folks that had dogs...and there was an awful lot of air freshener in the RV - they must have bombed before they sold and tried to de-stink the chemicals when I came to buy it. Getting my education

 

[Gizmo100]

Those are some big fleas...or you are really zoomed in on them.

 

[Horsemen]

LMAO

 

[Horsemen]

We have combustion - and HEAT!!! Thank you very much everyone. I learned A LOT from all of you good folks - and feel very confident I could solve another furnace problem quickly.

Many many thanks!!!!!