Furnace Problem

[R.S.O'Donnell]

Ours did the same as you describe early on. Everything seemed to be fine. Only when I unscrewed the ignitor/flame sensor and reinstalled it did it work normally. I suspect it was some sort of a connection issue that made it "think" there was no flame.

[Coug60]

Originally Posted by jsb5717

I've learned that just about anything is possible. It's possible that there's something wrong with your fan so that there is reduced air flow. However, I'd be more inclined to look again at the sail switch. Does the new one look exactly like the old one? Does the old one work when pressed in your hand? I've seen new sail switches just not work very well. Did you buy an OEM or aftermarket switch? Did it have good ratings? Sometimes they can work when vertical but not horizontal. Sometimes the sail just needs a little tweak to better catch the air.

I jumpered the Sail Switch, no change...

[Coug60]

A friend of mine brought up Altitude...
Has anybody had issues with Altitude with there furnace? I was boon-docking at about 10600ft and my home is at almost 7kft.

I wonder if my gas regulator in the furnace needs an adjustment for altitude.

[Bourbon County]

There are drawbacks to just firing a parts cannon at a problem. The first is obviously the cost of the parts and labor to install. The second is the possibility of introducing another problem because of installing the wrong part or installing incorrectly.

These furnaces are designed to operate at gas pressures between 11 to max of 14 inches in a water column. That converts to about 0.4-0.5 PSI, a very low pressure. Unless you have a manometer to measure pressures in this range, I would highly recommend not adjusting the regulator. It's true that pressures may need adjustment at high altitudes sometimes.

There are 2 blowers on the furnace; one is the main circulating blower for the warm air, the other is a draft induction blower that supplies air for combustion. The latter is the air stream the sail switch is located in. If the draft induction blower starts upon a call for heat, the thermostat is good. The blower starts and runs for about 15 seconds to purge any unburnt fuel that might be present. Prior to this purge the control board checks for the sail switch to be open. After the purge cycle, the control board checks for the sail switch to be closed which proves you have combustion air. Once combustion air is proven, the igniter is energized and the gas valve opens. After another time delay of 5-7 seconds the control board checks the flame sensor to prove the burner is lit. If it doesn't sense flame at that time, it will shut down. Once flame is sensed, the ignitor will turn off, the flame should be self sustaining at this point. It will then try 2 more times to restrike before shutting down for a period of time.

If the burner does fire, the sail switch contacts must remain closed throughout the burn, if you should lose it, the furnace will shut down. If it fires initially, the sail switch is good. It is possible the contacts will open during the burn, but not very likely.

The next step in the sequence if the burner fires and sustains flame would be the circulation blower starting. I don't remember if it's a time delay or maybe an internal temp sensor in the furnace. The reason for this delay is to minimize the initial blast of cold air when the blower starts. The high limit switch is the safety that will shut the furnace down should the circulation blower fail and the heat exchanger over heats.

From the symptoms you have described, it sounds very much like the flame sensor. These are pretty sensitive and the mounting location is critical too. If you are getting the purge cycle on the induction blower and the burner is actually lighting and shutting down in a few seconds, I'm pretty sure that's the problem. It's possible it's dirty; I would be very careful trying to clean it. Maybe just a Q-tip dipped in alcohol.

I believe the flame sensor is sold along with the ignitor on the same module if you choose to replace it.

[rames14]

We had a furnace issue from the start. Would attempt to start 3-4 times and finally go, until it didn’t. After checking everything, while putting it back together the mobile tech found the igniter screw was stripped. Put in a larger screw and haven’t had an issue since. The igniter screw is also the ground.

[jeffba]

jumpering the sail switch doesn't help. The furnace looks for the state change of teh switch

[Daryles]

Originally Posted by Coug60

A friend of mine brought up Altitude...
Has anybody had issues with Altitude with there furnace? I was boon-docking at about 10600ft and my home is at almost 7kft.

I wonder if my gas regulator in the furnace needs an adjustment for altitude.

My post #8 above.
If your burner actually fires then shuts off, repeat, the manual calls that "Limiting".
I would suspect Limit switch, flame sensor and control board.
The flame sensor is integrated with the sparker

Flame sensor testing

https://www.youtube.com/watch?v=8XucClM6bJQ

You can jumper the limit switch for troubleshooting.

Lots of good YouTube videos.

[GreG L.]

I had almost the same symptoms and replaced everything with no luck, until I noticed a light on in the fuse panel and then it went out. What was happening is the 15 amp black fuse is a auto reset fuse for the furnace and it went bad causing it to heat up prematurely and then reset at different intervals depending on how hot it had gotten, replaced it with a blue 15 amp and all worked.

[firestation12]

As a few others have alluded to, the igniter prong performs 2 functions….a high voltage created from the control board, jumps from the prong to the metal burner. If ignition properly takes place, the flame creates a pathway for a small voltage to flow from the prong to the grounded metal burner. The control board senses this millivolt current and interprets this as confirmation the burner is lit and allows the gas valve to continue to operate. A poor ground from the metal burner frame to the control board can prevent that millivolt to be sensed. An excessive gap between the igniter prong and the burner can also cause the gas flow to shut down. FYI when ordering a new control board, I prefer the Dinosaur brand replacement. They have a great track record for their after marker boards.

[Coug60]

So got the new control board in and no joy..... same problem.
So i reviewed everything that I had done.
In no particular order for this post I:
1. Jumpered the Sail Switch (there's a trick to it), No Joy.
2. I jumpered the Limit Switch, No Joy.
3. I checked the Burner Head, looked clean and new, No Joy
4. I checked the gap between the Electrode Points, 1/8th inch verified with 1/8inch allan wrench, No Joy
5. Replaced the Control Bord with a new one, No Joy

So a little voice in my head brought me back to the Electrode, the only thing I did not override in the system. So I pulled it out again and gave it a further inspection. The electrode points looked good, not corroded nor burnt and it was lighting the gas. The only thing and to this day I wouldn't have thought anything of it, the base plate of the Electrode was completely discolored (not rusted or dark, yellowish). So with a new on on hand I replaced it and BAM, everything worked like it should... Not sure if that had anything to do with it, might have just been the manufacturing process.
SO... after all that shut everything down and went inside patting myself on the back. A hour or so later went back outside to the RV to admire my work and started the furnace up and again I have the problem back... I have no idea what it is at this point. I can hear the Electrode sparking and lighting the burner and it catching, but something is shutting down the gas but not fan as usual. I replaced the regulator with a new bad one I found out so put the old one back in (gas leak on the right hose),

I have an appointment for next Monday for a tech to come out...

[Coug60]

Hey Bourbon Country
Check my last post.

[Coug60]

Hey Dayles... Thanks much for the video, might try that this weekend.

[jsb5717]

Still could be the propane regulator.

[rames14]

Coug60, two things I didn’t see on your list. Did you replace the 15 amp resettable fuse with a standard blue 15 amp fuse and did you make sure the igniter screw tightens down (ours was stripped).

[firestation12]

Originally Posted by Coug60

So got the new control board in and no joy..... same problem.
So i reviewed everything that I had done.
In no particular order for this post I:
1. Jumpered the Sail Switch (there's a trick to it), No Joy.
2. I jumpered the Limit Switch, No Joy.
3. I checked the Burner Head, looked clean and new, No Joy
4. I checked the gap between the Electrode Points, 1/8th inch verified with 1/8inch allan wrench, No Joy
5. Replaced the Control Bord with a new one, No Joy

So a little voice in my head brought me back to the Electrode, the only thing I did not override in the system. So I pulled it out again and gave it a further inspection. The electrode points looked good, not corroded nor burnt and it was lighting the gas. The only thing and to this day I wouldn't have thought anything of it, the base plate of the Electrode was completely discolored (not rusted or dark, yellowish). So with a new on on hand I replaced it and BAM, everything worked like it should... Not sure if that had anything to do with it, might have just been the manufacturing process.
SO... after all that shut everything down and went inside patting myself on the back. A hour or so later went back outside to the RV to admire my work and started the furnace up and again I have the problem back... I have no idea what it is at this point. I can hear the Electrode sparking and lighting the burner and it catching, but something is shutting down the gas but not fan as usual. I replaced the regulator with a new bad one I found out so put the old one back in (gas leak on the right hose),

I have an appointment for next Monday for a tech to come out...

As I stated in post #29, a poor ground can cause a shutdown. The ignition rod is trying to pass a MILLIVOLT through the flame which then has to be sensed at the mother board. The slightest resistance will offset that itsy bitsy current from being sensed. All components of that millivolt circuit should be suspected, including the ignition wire, its connections, and of course all of the burner’s metal mounting points. Using a jumper wire consisting of alligator clips at each end to bond the burner assembly back to the mother board would be worthwhile effort. In replacing the base plate, you seem to have temporarily corrected that missing millivolt pathway.

[STAbraham]

I'm not sure if anyone added this info. We also had furnace issues, but believe that it was LP pressure related. Changed tank and hit reset inside of panel and the issue appears to be resolved. But, the interesting thing for us, was that thermostat in the bedroom. We have a 2020 and it's a 4 seasons. My wife was checking that thermostat, and asked why it said "Heat pump". We set the thermostat and put it on the heat pump setting, and low and behold, we got heat from the upper vents via a heat pump. Our dealership never advised that we even had a heat pump. I had to go online, look up our specific unit, and it shows that it has a heat pump off of the main A/C unit. It heats up the bedroom nicely, and definitely saves on the use/cost of propane. Thought I would pass along, in case you might have the same situation. Good luck and God Bless!! 🙏🏼

[rames14]

Abraham, you will want to download the Keystone App. It has your manuals and information on all of your systems. Some dealers don’t equip their customers with the information they need. And if you haven’t already done it, change out your 15 amp fuse.

[Carl n Susan]

STAbraham: It helps immensely if you post the year and model f your Montana. Adding that info to your Signature ensures it is available on every post. (https://www.montanaowners.com/forums...ad.php?t=70323 Post #23)

I assume you have some type of rear bedroom model. The main AC is always the rearward one and in this case the thermostat is near the bedroom. The main AC has had a heat pump for several years where the front AC (in your living room?) does not.

[Coug60]

Originally Posted by rames14

Coug60, two things I didn’t see on your list. Did you replace the 15 amp resettable fuse with a standard blue 15 amp fuse and did you make sure the igniter screw tightens down (ours was stripped).

Yes, have a regular fuse in and everything is tight...

[Coug60]

Originally Posted by Carl n Susan

STAbraham: It helps immensely if you post the year and model f your Montana. Adding that info to your Signature ensures it is available on every post. (https://www.montanaowners.com/forums...ad.php?t=70323 Post #23)

I assume you have some type of rear bedroom model. The main AC is always the rearward one and in this case the thermostat is near the bedroom. The main AC has had a heat pump for several years where the front AC (in your living room?) does not.

I was told Heat pump is for above 50Degs and Furnace below 50Degs.
My AC therostat is in the rear bedroom and my furnace theromastat is in the kitchen nect to the panty on the wall.