2019 E-Pro 15TB Furnace - No Flame

[Billy1987]

Looking for some help with my heater. We recently purchased a 2019 15TB. On our first trip with our 15TB this weekend we put the heat on. It came on the first time and worked very well. Then the rest of the night we did not have any heat. I've ran through the purge cycle in the manual, checked the 7.5A fuse, and looked for kinks in the hoses. I took the front cover off and can see a spark when it's trying to ignite but am not getting any pilot light through the sightglass. The propane is on and the stove burners and hot water hearter using propane work fine so I do not think it's a propane issue.

Any suggestions would be greatly appreciated!

[HangDiver]

Are you hooked up to shore power or are you running off your battery(ies)?

[Billy1987]

I have tried both. The model is a Suburban NT-20SEQ.

[HangDiver]

A common issue that happens with these is that there is not enough voltage provided to the furnace to run the fan at the minumum rpm required to activate the sail switch. Subsequently, the furnace will shut down and not relight.

When this happens, the furnace will light and run as expected. However, as the battery voltage runs down (the fan draws the battery down), there is not enough power to run the fan fast enough to open the sail switch and the furnace will no longer operate as expected. In fact, once the battery voltage drops to 12.2v (or there abouts), the furnace will shut down even though other lights and items running off the 12V circut will continue to operate.

This may explain what you experienced on your first outing. There could be another problem with your furnace but the low voltage issue is common to those of us just getting started with a new travel trailer.

Those E-Pros are nice campers. Congratulations on your purchase and welcome to the forum.

[Billy1987]

Thank you! I can check the voltage across the battery. I believe the sail switch is working properly. My understanding is if that's not working then it wouldn't make it to the ignite stage. It's attempting to ignite but I'm not getting a flame. From what I see it may be the board or the solenoid for the propane.

Thank for for the congratulations as well!

[HangDiver]

When you get it figured out please post up what you did to fix it.

Good luck.

[Larry-NC]

Originally Posted by Billy1987

Thank you! I can check the voltage across the battery. I believe the sail switch is working properly. My understanding is if that's not working then it wouldn't make it to the ignite stage. It's attempting to ignite but I'm not getting a flame. From what I see it may be the board or the solenoid for the propane.

Thank for for the congratulations as well!

If it's not a battery issue, there are a couple of things that can cause ignition issues. Using a blower forcing air into the combustion chamber (like a turbocharged car) makes for a system that is pretty sensitive to the fuel-air mixture.

• One problem, regularly reported, is a restriction in the air circulation in the combustion air flow. Mud daubers love to build mud nests in the air intake/exhaust ports on the side of the trailer. This is pretty easy to diagnose, with a flashlight or a borescope, or even probing with wire from a coat hanger.
• Another problem that actually happened in our smaller trailer was failure of the propane regulator, at the tanks. The furnace motor has a shaft at each end. One end drives the blower that charges the combustion chamber. The other end drives the blower that circulates air through the heat exchanger and trailer. The turbocharge scheme makes the furnace very sensitive; it requires a stoichiometric mixture. When the regulator starts to fail, the gas pressure actually increases. Ours would ignite with the front cover off, but not with it on.
  
  My guess was that with the front cover off there was less resistance from the heat exchanger circuit, the blowers ran faster, and there was enough added air to match the increased fuel. Ultimately, I found that the regulator was delivering 14" w.c., rather than the specified 11" (about 1/2 psi). Of course the range has a secondary regulator to further reduce the pressure so no problem was seen there. The refrigerator has a tiny orifice and is tolerant of pressure changes. Pretty unusual, but I suppose your new regulator could have suffered "infant mortality."
• There is an overtemperature switch ("limit switch") mounted by the front cover. If the furnace gets too hot, it opens. The gas valve closes but the blower continues to run, to cool the furnace off. When the furnace cools, if the thermostat is still calling for heat, it goes through another ignition cycle. Of course if this limit switch has stuck open (or its circuit is open), the ignition won't occur, just as your symptom. Check continuity of this switch or temporarily bypass it.

I've uploaded the Service Manual.