Furnace Failure after Power Outage

[Thiss]

Furnace failed after a power outage. I was away from the unit, but heard of the power being out in the area. My uneasy feeling won and I drove 93 miles in the best ice and wind storm of my life; it was event free.

Got to camp. Door frozen. Patients and body heat got the lock open. Got I to the unit (Nimbus is its given name) and “oh no” it’s cold inside. Go to the thermostat and all appears as left. Therm was set to “Auto” 45f. Turn up the temp setting. Furnace blower runs, no ignition and then quits. After some time checking the fuses, the breakers, turning off and on at the therm, checking the gas, running the stove to make sure of no gas line blocks, pulling the exterior furnace cover and hitting the reset button and checking the fault code (limit switch/airflow). Finally got it to reset by killing all power and hitting the battery disconnect switch to remove 12v from it. It fired right up after and ran normal through the night.

The plumbing froze. It thawed and no breaks observed. Water pump is on and indicating no loss of pressure.

Ok, here is where I need help: why didn’t my batteries take over and kee the furnace going? I checked batteries and they were full.

How can I avoid this in the future? My gut says that auto is the wrong thermostat setting and it should just be on heat pump. Inverter was off, but why would it be needed, isn’t the furnace 12v? I am going to try to recreate the power outage today and see what happens.

Lastly, I was scared off of my electric space heaters, but I think they are going to be redeployed in the future.

[Lily&Me]

Hmmm, me being likely the least knowledgeable person who may respond here 😅, I wonder if that you were plugged into electricity kept the battery from taking over?

Maggie

[Thiss]

I just killed 110 at the pole. Furnace still working. 13v of battery.

I have a dealer installed surge protector. I will check it for fault codes after turning 110 back on.

[BayouBiker]

Given that there were no fault codes even after "reset" I'm guessing the furnace ignition controller board firmware erasable memory portion got scrambled. Removing power completely for a longer duration cleared it and it operated properly after that. Probably a short stint of low voltage to the board along with voltage fluctuations through the thermostat circuit that occurred when power to the trailer was lost is what corrupted the machine level code stack in memory. Since the code was corrupted, no error codes....

[azflycaster]

There are numerous reasons why a furnace would fail. There is a fault indicator on the circuit card that would have given you a clue to the problem. Most common is a sail switch failure which could also be low 12 volts.

[ITSNO60]

Originally Posted by BayouBiker

Given that there were no fault codes even after "reset" I'm guessing the furnace ignition controller board firmware erasable memory portion got scrambled. Removing power completely for a longer duration cleared it and it operated properly after that. Probably a short stint of low voltage to the board along with voltage fluctuations through the thermostat circuit that occurred when power to the trailer was lost is what corrupted the machine level code stack in memory. Since the code was corrupted, no error codes....

Glad you got it going.
I'm going to go with what the other Brian says, often when power goes out or especially when it comes back up it can drop in and out multiple times wreaking havoc with circuit boards, this happens on my home AC, the fan will continue to run but the compressor will not come back on till I shut it's breaker off and reset it. This is a good reason to have a delay (my home unit does not and I need to fix that). My RV has a 2.5 minute delay through my PI EMS.

[TitusNW]

Check the outside circuit breaker. Turn off/on and retry the furnace


Steve

[Wazbro]

Originally Posted by Thiss

My gut says that auto is the wrong thermostat setting and it should just be on heat pump.

I don't have a newer AS with the single controls but, my gut says the furnace wont work when set to heat pump and it should be set to furnace for the furnace to run.

[Thiss]

Originally Posted by Wazbro

I don't have a newer AS with the single controls but, my gut says the furnace wont work when set to heat pump and it should be set to furnace for the furnace to run.

Wopse. Yes, that’s what I mean “Furn” is the best setting. No heat pump or auto for winter.

[richard5933]

One thing catches my eye and that's the mention of a heat pump. Those typically run on 120v only, not 12v (although 12v might be needed to run the controls).

If the goal is having a heating system that works in situations where you're not plugged in, then I'd remove the heat pump from the system and stick with the propane furnace. As long as you have propane and your batteries are charged you'll have heat if it's working.

Also, the heat pump is not going to do much for warming the plumbing located below the floor, but the furnace will.

[Thiss]

Originally Posted by richard5933

One thing catches my eye and that's the mention of a heat pump. Those typically run on 120v only, not 12v (although 12v might be needed to run the controls).

If the goal is having a heating system that works in situations where you're not plugged in, then I'd remove the heat pump from the system and stick with the propane furnace. As long as you have propane and your batteries are charged you'll have heat if it's working.

Also, the heat pump is not going to do much for warming the plumbing located below the floor, but the furnace will.

I had it set to Auto thinking I could have it all. The furnace for freezing temps and the heat pump for the warmer daytime tempt to save a bit of propane, but now we are going with just the straight furnace. I think you are right that each system having a different power requirements could have been a contributing factor to the furnace getting thrown off whack either when the power was out or when the power came back on.

[clarklaflare]

Originally Posted by Thiss

why didn’t my batteries take over and kee the furnace going? I checked batteries and they were full.

How can I avoid this in the future? My gut says that auto is the wrong thermostat setting and it should just be on heat pump. Inverter was off, but why would it be needed, isn’t the furnace 12v? I am going to try to recreate the power outage today and see what happens.

Lastly, I was scared off of my electric space heaters, but I think they are going to be redeployed in the future.

Since the furnace does run off the 12 volts batteries, the most likely scenario is that when power was lost, the converter stopped charging and the battery voltage eventually dropped below the threshold required for the furnace to continue running. When power restored and recharged the batteries the low voltage shutdown smarts in the furnace controller still required a hard reset to recover.
Regarding the thermostat Auto setting, understand that this is a fan-only control for the A/C and has nothing to do with mode selection. You must change modes manually. If the thermostat is displaying Auto, it is in Fan mode and the furnace would never come on.
Space heaters on outlet thermostats and remote temperature monitoring would be your best safeguard.

I realized later that the op was probably referring to AUTO Change-over Mode. In this, case disregard my comments regarding auto fan operation as they would only apply to a thermostat that does not support this mode.