Atwood furnace won't light.... EVERYTHING seems fine..

[kdanie]

I ran out of propane last Sunday night, refilled Monday morning & furnace won't relight. 3 blinks, 3 seconds, 3 blinks = ignition lockout.

Furnace is an Atwood 8940-LP-LD. It is mounted inside my "basement" on the utility flat. A real pain to get out & back in. I rebuilt it with all new parts 1.5 years ago. New blower motor, control board, gas solenoid valve, ignitor, burner, sail switch, high temp switch. So essentially everything but the tin housing and heat exchanger. Worked great for 1.5 years.

Everybody points to the sail switch, it's fine (checked with a meter & free of debris), high temp safety switch is ok too. I put it on the table, hooked up 12v battery & jumped the thermostat connection so it would "light". The fan comes on, I could feel the solenoid valve snap open, the ignitor start clicking, the solenoid valve close. I goes through 3 attempts to light (normal) & locks out. The control board is working... the high temp switch is closed, the sail switch closes, the board calls for fuel -valve open- igniter starts clicking but I smell no gas out the exhaust so no fuel is getting in/out.

I just replaced my auto switching propane regulator (10 years old), some people say they can go bad if your tanks are empty & refilled/opened. Still no propane getting to the burner. I'm now thinking the gas solenoid is bad/plugged up somehow even though I can feel both valves snap open and close as it tries to light.

I'm super frustrated after emptying the basement twice, pulling & reinstalling the furnace twice with no change in condition. I need a "thought check" on my logic. Am I overlooking something??

Ken

[kdanie]

After thinking some more I'm going to remove the furnace AGAIN & pull the burner assembly & check the orifice. I'll be sure to write my SN down again just in case. Seems the only thing left. The burner assembly is a pain to get out due to the long propane tube across the top of the housing, last time it was REALLY tight.

ken

[emm-dee]

Originally Posted by kdanie

After thinking some more I'm going to remove the furnace AGAIN & pull the burner assembly & check the orifice. I'll be sure to write my SN down again just in case. Seems the only thing left. The burner assembly is a pain to get out due to the long propane tube across the top of the housing, last time it was REALLY tight.

ken

You might want to hold off on doing all that work. If you ran the furnace until it ran out of propane then sometimes it can take a while to purge all the air out of the lines. On a lot of RVs the furnace is the appliance mounted the furthest from the supply.

Suggestion: light the stove and oven first and let them burn about 15-20 seconds. With the stove still lit, light the gas water heater, followed about 20 seconds later by the refrigerator. After 30 seconds or so turn all appliances off and then start the furnace.

Can’t hurt and it’s very likely the furnace will light. Running out of propane while an appliance is operating has the same result as turning the propane supply valve off while an appliance is lit. The appliance(s) will use all the propane left in the line which requires purging the air before use. I’ve had it happen a couple times when switching between built in and external propane supplies. One cannot have both systems open at the same time so there is a short time when transitioning that there is no gas flowing. It doesn’t take long for purging of air to be required if an appliance is operating during the switchover.

[kdanie]

Ran the stove before I tried the furnace. The water heater was up to temp on electric and didn't light, same with refer. The furnace is the furthest by about 8 feet (opposite side). I did bleed the propane at the fitting on the furnace so it's only about 2 feet of tubing across the top to the solenoid. I gave it 3 restarts with 3 ignition cycles each, that should easily purge the 2 feet of tubing.... I hope.

ken

[kdanie]

Well... That was disappointing.. Pulled the furnace again, removed the burner/solenoid assembly. The orifice is like new (1.5 years old). I pulled the solenoid off the assembly, hooked up some 12v & ground to it, the solenoid opened as expected & I could easily blow through it. Reinstalled everything, adjusted the spark gaps a bit, they were a little close. Hooked up the burner assembly outside the furnace & tested it, electrodes sparked, solenoid valve opened, reassembled it all. Tested on the bench again, everything works fine. Also blew through the 2' propane tube/90* fitting that goes in the top of the solenoid valve. Reinstalled the furnace, purged the gas line, lit the stove & tried the furnace. Still can't smell any propane in the exhaust, no ignition. I can still hear the solenoid valve opening & the electrodes sparking.

SOOOO... it seems it still a propane supply issue. It's rigid copper line across the utility flat and down to the tank space. It worked fine now zip. I'm at my wits end.

I guess I'll have to put together a way to measure gas pressure at the furnace inlet, Atwood calls for 11" of water pressure. Time to hit the hardware store.

[emm-dee]

Originally Posted by kdanie

Well... That was disappointing.. Pulled the furnace again, removed the burner/solenoid assembly. The orifice is like new (1.5 years old). I pulled the solenoid off the assembly, hooked up some 12v & ground to it, the solenoid opened as expected & I could easily blow through it. Reinstalled everything, adjusted the spark gaps a bit, they were a little close. Hooked up the burner assembly outside the furnace & tested it, electrodes sparked, solenoid valve opened, reassembled it all. Tested on the bench again, everything works fine. Also blew through the 2' propane tube/90* fitting that goes in the top of the solenoid valve. Reinstalled the furnace, purged the gas line, lit the stove & tried the furnace. Still can't smell any propane in the exhaust, no ignition. I can still hear the solenoid valve opening & the electrodes sparking.

SOOOO... it seems it still a propane supply issue. It's rigid copper line across the utility flat and down to the tank space. It worked fine now zip. I'm at my wits end.

I guess I'll have to put together a way to measure gas pressure at the furnace inlet, Atwood calls for 11" of water pressure. Time to hit the hardware store.

That’s a hard one to figure out. One of four lines not supplying adequate pressure is rare. Let us know the solution when you find it.

Edit: I just read an interesting thread which you should check out. It could have info relevant to your problem.

https://www.forestriverforums.com/fo...ml#post2722606

[kdanie]

Thanks, that MAY be the issue. I'll check the pressure soon. If it's low I'll at least have more to look into.

ken

[Larry-NC]

Originally Posted by kdanie

Well... That was disappointing.. Pulled the furnace again, removed the burner/solenoid assembly. The orifice is like new (1.5 years old). I pulled the solenoid off the assembly, hooked up some 12v & ground to it, the solenoid opened as expected & I could easily blow through it. Reinstalled everything, adjusted the spark gaps a bit, they were a little close. Hooked up the burner assembly outside the furnace & tested it, electrodes sparked, solenoid valve opened, reassembled it all. Tested on the bench again, everything works fine. Also blew through the 2' propane tube/90* fitting that goes in the top of the solenoid valve. Reinstalled the furnace, purged the gas line, lit the stove & tried the furnace. Still can't smell any propane in the exhaust, no ignition. I can still hear the solenoid valve opening & the electrodes sparking.

SOOOO... it seems it still a propane supply issue. It's rigid copper line across the utility flat and down to the tank space. It worked fine now zip. I'm at my wits end.

I guess I'll have to put together a way to measure gas pressure at the furnace inlet, Atwood calls for 11" of water pressure. Time to hit the hardware store.

It's not 11" of water pressure. It's the amount of pressure (e.g., gas pressure or air pressure) that would displace a column of water 11". That corresponds to around 1/2 psi. or about what you breathe out.

The illustrations show the manometer I built from scraps and about $3-4 of hardware from Lowe's. There is water in the U-shaped tube and one drop of food coloring for visibility. The backboard has lines every 1/2", but they are labelled as 1". This because, after you start with both tubes of water at 0", the pressure moves one water level down 5-1/2" and the other water level up 5-1/2", corresponding to the 11" requirement.

[kdanie]

Thanks, I DO understand a manometer, used them a LOT on diesel engine performance monitoring in my younger days. I have the parts I need to build one now but it's too rainy to empty the basement to get to the furnace to test it.

ken

[Larry-NC]

Originally Posted by kdanie

Thanks, I DO understand a manometer, used them a LOT on diesel engine performance monitoring in my younger days. I have the parts I need to build one now but it's too rainy to empty the basement to get to the furnace to test it.

ken

Ken,

Sorry. I didn't mean to talk down to you. It's hard to guess the experience of another forum poster. Bad things can happen if you don't give a novice enough information, so I err on the verbose side.

Larry

[dahagen]

Went through the same things on my furnace you did. Sail switch worked, blower powered on with 12 V. A repair guy said change the circuit board. $100 Dinosaur from Amazon. Fixed the problem. Didn't have to remove the furnace to do it.

[kdanie]

Originally Posted by Larry-NC

Ken,

Sorry. I didn't mean to talk down to you. It's hard to guess the experience of another forum poster. Bad things can happen if you don't give a novice enough information, so I err on the verbose side.

Larry

No problem. More info is better than not enough.

ken

[kdanie]

Well, poop... I built a manometer & hooked it up... I had a "bit" more than the minimum 11" of water column-the propane blew all the water out all over the basement so lack of propane pressure isn't the issue, no "goop" plugging the line.

I hooked the propane line back up and... it fired right up normally. I suspect menehunes... No logical explanation on why it refused to fire for a couple weeks. It's the warmest day we've had in a long time so maybe that helps?? Don't know..

ken

[5picker]

Originally Posted by kdanie

Well, poop... I built a manometer & hooked it up... I had a "bit" more than the minimum 11" of water column-the propane blew all the water out all over the basement so lack of propane pressure isn't the issue, no "goop" plugging the line.



I hooked the propane line back up and... it fired right up normally. I suspect menehunes... No logical explanation on why it refused to fire for a couple weeks. It's the warmest day we've had in a long time so maybe that helps?? Don't know..



ken

A thought about your observations... I've read a few posts over the years about LP tanks that were refilled with a mixture of LP and Butane.

When those tanks were used in cooler/colder climates, (like filled in FL and then used up north) many of the LP appliances did not work or worked correctly.

I'm wondering, since you mentioned you ran out of propane and had the tank filled, maybe you got some incorrect mixture? Now that it warmed up, that mixture boils off better than it did when cooler?

Just a thought...

[chriscowles]

Originally Posted by kdanie

Ran the stove before I tried the furnace. The water heater was up to temp on electric and didn't light, same with refer. ...

This is well after your issue is resolved but you can always get the hot water heater to kick in by running some hot water down the sink. The thermostat will sense the temperature change of the incoming cold water.

The refrigerator will react similarly to leaving the door open, but you might not want to do that if you're actually trying to keep the food cold.

[kdanie]

We've been on the OR coast for over a month and have refilled here before with no issues. It's definitely a strange problem.

Last Sunday I had to move out of the park to renew my brakes so I went about half a mile away to an old parking lot at a soccer field on the back side of a neighborhood, 3 hours later the brakes/hubs are all new. The 'fridge ran well while we were down there.

I hate it when there is no definitive solution, but in this case I'll take it just working again.... Magic???

ken

[Larry-NC]

Originally Posted by kdanie

Well, poop... I built a manometer & hooked it up... I had a "bit" more than the minimum 11" of water column-the propane blew all the water out all over the basement so lack of propane pressure isn't the issue, no "goop" plugging the line.

This surprises me. When I did this with a failing regulator (over 14" w.c.), the level was wrong, but it never blew water out of the manometer.

The reason why the furnaces (at least Suburbans) are so finicky is that they are supercharged. The range, water heater, and refrigerator simply burn gas. The air supply is convection, nothing mechanical. Not much to go wrong--in fact the one thing that goes wrong is disruption of the air supply caused by spider webs, etc.

But the furnace is supercharged by the forced air from the fan. Getting the right "stoichiometric" fuel/air ratio is important for these units. When mine was getting too much fuel, I found that opening the plenum changed the fan speed enough that it would light; changing the regulator fixed the problem.

[kdanie]

Another update: It worked fine for about a week then would not start. Just got dry enough weather to empty out the basement & check it out again. No it seems to not even spark or the propane solenoid doesn't activate. I'll pull it out again when I get motivated & check the burner & solenoid functions. Maybe the control board is bad now. I'll be in Pasco WA next to Broadmore RV, maybe they have one in stock.

[kdanie]

So, I pulled out the wall to the basement today. Cycled the furnace & the propane solenoid did not open. I pulled the furnace out & removed the solenoid/burner assembly & put power directly to the solenoids-worked fine. Re-installed the burner/solenoid assembly & cycled the furnace-spark but no solenoid clicking. I pulled the control circuit board & tapped on the box I THINK is the solenoid relay, reinstalled it, put power to the furnace & the solenoids functioned fine. Reinstalled the furnace & it fired up normally. I will get a new circuit board in a week when I'm next to a big RV dealer/parts/service place. I probably have the old, still good, board that I replaced 2 years ago when I went through the entire furnace but it's in storage a long ways away.

It makes me crazy when the symptoms aren't consistent-makes it hard to troubleshoot logically.

Ken

[mmartin_tdc]

Instead of going OEM on the board, I would recommend the Dinosaur replacement boards.
Much better quality that stock, in my opinion, and slightly less expensive to boot.