Furnace only ignites with very full battery

[bajaphile]

Hi all,
I am trying to figure out what might need to be checked or cleaned to fix my furnace "issue".

As long as I have 12.5 to 12.7V on my house battery bank (I have 2 brand new group 31 deep cycles), the furnace blower will kick on and then ignite the burner. Great.

Through the night as it is cycling on and off, it will stop igniting and essentially shuts off completely. I'll play with the thermostat a bit and blower will turn on for 15 seconds or so, then fail to ignite burner. This has happened a few times and I noticed that it is directly related to how much voltage it is getting. After cycling through the night it drains the batteries down far enough to about 12.3V.

Once the solar kicks in, or I start the truck, the furnace will operate as normal.

What should I check here? I am new to RV furnaces. My assumption is that the blower motor is not providing enough air through some circuit and it is a safety feature that is preventing the burner to ignite. However I really would hope that 2 deep cycle batteries would handle at least a night!

Thanks for your help

 

[PokyBro]

Hi Bajaphile,

You didn't mention what furnace you have, so my suggestion and example might not be helpful.

I have an Atwood Hydroflame furnace, which I had trouble with it igniting, but not necessarily when battery was lower. The blower would come on for 30 seconds, but it would fail to ignite, the shut off. On the Hydroflame later models with direct spark ignition DSI, there is a circuit board on the lower front. When you take it off and look behind there is a led red light that flashes at different intervals. There is a label that tells you what to suspect is the area of the furnace malfunctioning. For example a flash with a 2 second pause and then another flash might mean the sail switch. You try starting the furnace and watch for the flashing light.

The sail switch is a very common problem for malfunction and potentially could be affected in your case by the fan not blowing at the same speed or intensity when your battery is a little lower, not sure, but if you have a label with a grid identifying what the problem is, then you could replace the sail switch as an example.

If that is the part, its fairly easy to get to on the Hydroflame, as described in my thread below. If you have a Suburban, it might be the same part, but I'm not familiar if it has a diagnosing flashing light or not. If you were to determine what part is malfunctioning, you can look up the part number on an owners manual, and do a google or amazon search, and be able to order it that way.

Anyhow, take a look at might thread, and see if it is helpful. Good luck with identifying the problem. Others may have additional suggestions.

https://www.wanderthewest.com/forum/topic/12116-new-build-1981-grandby-to-become-a-hawk/page-25


Poky

 

[bajaphile]

Thanks Poky for your reply! I guess I'll just have to dive in and give it a look.

It is a Suburban DD-17DSI , I had forgot to mention that!

 

[craig333]

On mine I adjusted the ignitor and it lights much easier now. I also had the issue of mine not working with low voltage. I solved that by getting good batteries and charging them appropriately. I'll end up in the morning no lower than 12.8v even running the heater all night.

 

[Vic Harder]

12.2 volts after just one night, just running the furnace with dual batteries? Is that under load (while the furnace is trying to start) us just sitting there? Seems awfully low..
https://electronics.stackexchange.com/questions/401414/calculate-battery-state-of-charge-percentage

You might have a problem other than your furnace. Hard to tell without a good battery monitor, like the Victron 712 BMV.

 

[bajaphile]

Well, I guess I was wrong... furnace is still not igniting even with 13V or when engine is running. It is really just hit or miss. It ignites and runs great about 25% of the time. Otherwise the fan just kicks on and I never hear the ignition to turn the burner on.

Sail switch looks ok and it is definitely moving when the fan comes on (I can hear the click too). The way my Hawk is setup I will need to remove the entire front panel of my cabinet area to properly unfasten the furnace. Bummer.

Going to keep researching and see what would be causing my intermittent issue.

As far as the batteries, we went and camped last night and with just lights on, occasional water pump and charging phones, I woke up to 12.6V, which is acceptable to me. I used my ammeter and it appears that the CO2/LP gas monitors pull 0.4A. I just got some Duracell 31M deep cycle batteries, flooded cell. I had good luck with them in the past, but maybe they are crap now. They are only about $130 each which makes me question their quality. What is the favorite battery type here?

 

[craig333]

Dinosaur has a pretty good reputation for aftermarket parts. https://www.dinosaurelectronics.com/Tips_Tricks_Page.htm

Batteries are particular in their charging requirements.If the manufacturer specs a 14.8v bulk charge and your solar is set for 14.5 you won't get the best performance from them. One of the reasons its preferable to get an adjustable charge controller.

They seem decent, made by East Penn but oddly enough in my ten minute google search I couldn't find charging specs anywhere. Even here it doesn't say.
https://www.driveduracell.com/battery-care-maintenance

 

[Vic Harder]

Well, I guess I was wrong... furnace is still not igniting even with 13V or when engine is running. It is really just hit or miss. It ignites and runs great about 25% of the time. Otherwise the fan just kicks on and I never hear the ignition to turn the burner on.

Sail switch looks ok and it is definitely moving when the fan comes on (I can hear the click too). The way my Hawk is setup I will need to remove the entire front panel of my cabinet area to properly unfasten the furnace. Bummer.

Going to keep researching and see what would be causing my intermittent issue.

As far as the batteries, we went and camped last night and with just lights on, occasional water pump and charging phones, I woke up to 12.6V, which is acceptable to me. I used my ammeter and it appears that the CO2/LP gas monitors pull 0.4A. I just got some Duracell 31M deep cycle batteries, flooded cell. I had good luck with them in the past, but maybe they are crap now. They are only about $130 each which makes me question their quality. What is the favorite battery type here?

Favorite type? AGM, true deep cycle, not dual purpose. If the battery specs list a "cold cranking amps" number, they are dual purpose and not ideal for solar use. Lithium is coming on strong if you can stomach the initial purchase price shock. Overall, LiFePo4 batteries cost less if you are keeping your camper for 5+ years.

Favorite brand? Depends. LiFePo4 = Battleborn. AGM - Trojan, Rolls are good brands.

12.6 after use over night is fine, even if that is your "at rest" reading. I'd still recommend a true battery monitor, not a volt meter or ammeter. Otherwise you are just guessing.

The batteries are unlikely to be why your furnace isn't lighting up, given what you have told us so far.

 

[New to campers]

Hello, we recently purchased a used 2000 Hawk 4 Wheel Camper. The furnace worked fine at first. Now, when we turn it on it ignites stays on for 5 or 6 seconds and the shuts off. Then, we will try it again after a few hours and it will start right up again. Any suggestions on what might be wrong with this intermittent problem?

 

[larryqp]

Does it really ignite, meaning the burner lights? If the burner isn't lighting, then check the sail switch. Stan of FWC has a number of good videos on Youtube addressing furnace troubleshooting.