Furnace ignites, goes out, ignites, out

[csper29605]

Originally Posted by Bama

I disconnected the propane for about ten minutes. Reconnected to propane tanks then very slowly opened the valves. Used stove to bleed air out of the lines. Furnace is still doing the same thing.

I looked in exhaust tube from outside the camper and do not see anything. Since Jayco did not install an outside access door for the furnace, looks like I may have to pull the furnace to check the wires and tubes inside the furnace.

Thanks for all the tips on what to check. I will report back when I find the problem.

Bama

Hey did you ever figure out what is wrong with your furnace?? Our furnace just started to do the same thing. It work last night just fine and now it is doing the same thing.

[Jmac000]

If your furnace is firing, but not staying lit, here are some general things to check.

Make sure the ground wire is in good shape (grounding is very important)

Check the pilot orifice and pilot tube, make sure no bugs or anything is blocking it.

Check the thermocouple

Check the gas valve, is it getting and maintaining the proper voltage

check the combustion hose, is it plugged or collapsed

Blower running slow, filter blocked?

do you have a limit switch? are all the registers open and the return air NOT blocked

possible water in the propane, with these low temps, condensation frozen in the hose?

burner or pilot plate gaskets not sealed

sail switch defective

Is the furnace gas pressure at least 11.0" of water column with other appliances running?

you'll need a U-Tube manometer to check the gas pressure and voltmeter to check some of these things

[Bama]

Originally Posted by csper29605

Bama

Hey did you ever figure out what is wrong with your furnace?? Our furnace just started to do the same thing. It work last night just fine and now it is doing the same thing.

No I have not figured it out. I have called a two onsite service technicians. One would not work on it and the other stood me up two days in a row. I am still under warranty so I am going to have the dealer look at it next time I have it in for service. I called Jayco and had it documented it needs repair. I have tried everything that has been suggested short of pulling the furnace. Just not enough room where it is located for me to pull the furnace. Sure wish I had the exterior service door!

[Sunflake]

Ok guys, there is no thermocouple in these newer furnaces. You don’t have a standing pilot furnace. It’s spark ignition. If the furnace lights and burns for 2 seconds then it’s not likely it’s the sail switch because that switch has to be closed before it tries to light. Most likely is the flame sensor is having issues. Your furnace at home will do the exact same thing if after the burners light and that sensor doesn’t “see” flame then it shuts the gas valve off and recycles the system and tries again. If you can post a picture of the wiring diagram, if you have it would be helpful. If you have the owners manual for it let me know what brand and model furnace it is and I’ll se if I can look up the diagram.

[Jmac000]

Originally Posted by Sunflake

Ok guys, there is no thermocouple in these newer furnaces. You don’t have a standing pilot furnace. It’s spark ignition. If the furnace lights and burns for 2 seconds then it’s not likely it’s the sail switch because that switch has to be closed before it tries to light. Most likely is the flame sensor is having issues. Your furnace at home will do the exact same thing if after the burners light and that sensor doesn’t “see” flame then it shuts the gas valve off and recycles the system and tries again. If you can post a picture of the wiring diagram, if you have it would be helpful. If you have the owners manual for it let me know what brand and model furnace it is and I’ll se if I can look up the diagram.

is there a seperate flame sensor? or is it part of the spark ignition? is there a pressure switch?

[Sunflake]

I’d need to see the wiring diagram to be sure depending on how many burners are in the furnace it would be separate like your home furnace. But if it’s only one burner it could be all in one. I haven’t seen a pressure switch. Usually a sail switch. If someone with a newer furnace can post a Make and model I could see if I could find a wiring diagram. Also make sure there isn’t a wasp nest in the exhaust piping. That could mess with the sail switch. For some reason bugs/spiders love the smell of propane.

[hoppers4]

I was having the same problem and went on a search of the thermocouple. No such critter but there is a NC thermostat in the combustion chamber that's accessible from the outside. Apparently that thermostat needs to open within 2 seconds or the circuit board declares a fault. My thermostat worked fine as tested with a soldering iron. Never did determine what was wrong as it started working again. I suspect a flaky circuit board.

[Jim Smyth]

I had the same problem on mine. I have a 2017 28.5RSTS. I ended up disconnecting the furnace and was able to turn it 90 degrees so I could work on it under the cub-bard. I took the plate off the end to get to the mother board. They have that sealed pretty good inside the unit.



Once I got the metal panel off and had access to the mother board so I disconnected it and took it out. Now heres the weird part. There was a quarter sized green wet pubble under the circuit board and there was some what looked like green corrosion on the board.



This was on the underside of the board where literally nothing can get to it. Wasnt wet at all on the top or sides. So I located another mother board and put it all back together and it works like a charm. I cleaned the old bad board up and am keeping it for if this one fails to see if after the moisture was cleaned and dried if it still works.

[Sunflake]

Originally Posted by hoppers4

I was having the same problem and went on a search of the thermocouple. No such critter but there is a NC thermostat in the combustion chamber that's accessible from the outside. Apparently that thermostat needs to open within 2 seconds or the circuit board declares a fault. My thermostat worked fine as tested with a soldering iron. Never did determine what was wrong as it started working again. I suspect a flaky circuit board.

That “thermostat” is what’s called a high limit. It’s usually round about the size of a dine or Nickel. Has 2 wires attached. If the indoor blower motor quits working that safety gets hot and opens the circuit shutting down the gas valve. Under normal conditions you don’t want it to open.

[hoppers4]

That thermostat was on the combustion chamber side of the furnace right above the burner. Couldn't find a thermocouple or pile. There must be another stat some place else to detect low air flow/overheat on the house side. The motor is coupled to two fans. One inside air and one for the combustion chamber. Sail switch is also on the combustion side.

[Jmac000]

Originally Posted by hoppers4

That thermostat was on the combustion chamber side of the furnace right above the burner. Couldn't find a thermocouple or pile. There must be another stat some place else to detect low air flow/overheat on the house side. The motor is coupled to two fans. One inside air and one for the combustion chamber. Sail switch is also on the combustion side.

If it's right above the burner, its a Roll out switch (ROS) its there incase the burner has a backfire, the flame will hit that switch and turn off the gas. It's part of the safety circuit

has anyone posted the model # of this furnace? I have been looking for a schemtic but they hide them fairly well

[hoppers4]

Originally Posted by Jmac000

If it's right above the burner, its a Roll out switch (ROS) its there incase the burner has a backfire, the flame will hit that switch and turn off the gas. It's part of the safety circuit

Nice to know. Thank you. I'll also be on a quest for a schematic to figure out how the furnace does flame detection.

[TCNashville]

Originally Posted by hoppers4

Nice to know. Thank you. I'll also be on a quest for a schematic to figure out how the furnace does flame detection.

I think you'll find that the igniter has a dual purpose. Not only does it ignite the propane but also senses flame and sends that back to the board.

[hoppers4]

Originally Posted by TCNashville

I think you'll find that the igniter has a dual purpose. Not only does it ignite the propane but also senses flame and sends that back to the board.

Now that makes sense! That's one connection I didn't bother with on the circuit board as I figured if the igniter worked then the connection was good. If it's also a millivolt connection, then a bit of resistance at the board could reduce the voltage below the proper level. Thank you for the idea.

[Jmac000]

Originally Posted by hoppers4

Now that makes sense! That's one connection I didn't bother with on the circuit board as I figured if the igniter worked then the connection was good. If it's also a millivolt connection, then a bit of resistance at the board could reduce the voltage below the proper level. Thank you for the idea.

if the spark ignitor is also part the flame sensor, you can take some very fine sandpaper or something like a 3M pad and clean it. sometimes that works, sometimes it doesn't. Just be aware that Propane burns much hotter than Natural gas, so it tends to eat up flame sensors faster.

Here is a good explination of Flame rectification: If your interested in how this thing works, the ground to the furnace is critical in the flame sensor performance

https://www.hvactrainingsolutions.ne...rectification/

[Sunflake]

That’s what the limit switch you found does. If the fan quits or isn’t blowing enough air that switch opens

[hoppers4]

Originally Posted by Jmac000

Here is a good explanation of Flame rectification: If you're interested in how this thing works, the ground to the furnace is critical in the flame sensor performance

https://www.hvactrainingsolutions.ne...rectification/

This is the kind of info I live for. Very interesting read. I also see that it's microvolt vs millivolt which makes the connection and sensor cleanliness even more critical.

[hoppers4]

Originally Posted by Sunflake

That’s what the limit switch you found does. If the fan quits or isn’t blowing enough air that switch opens

I gather that you're talking about the sail switch. I had to replace that previously. I now have a different error code which indicates flame sensor failure. Now I know how the flame is sensed according to an article sent by Jmac000.

[Sunflake]

The other one on the combustion side, the round one.

[Sunflake]

Here is a wiring diagram. The sail switch is normally open. The round limit switch is normally closed