[ZekenSpider]

We have had a problem or two, but nothing like your experience. Glad your OK and that all the backup alarms worked.

We have a 2010 3326 with an NT-20SE furnace. We had to work on ours so I know quite a bit about the 2010 version. (the factory forgot to connect the air inlet and exhaust outlet pipes on ours so we had fumes and smarting eyes until I figured out the problem).

The control circuit in our NT-20SE has two safety shut-offs that will close the gas valve. The first is a "sail switch" in the combustion blower fan air stream. If this switch does not detect sufficient combustion air flow, it will not allow the gas valve to open (or will close it again if the air flow drops off). The second is an over temperature switch that will close the gas valve if the recirculating fan air internal temperature gets too high.

If either of these safety features activate, the control board locks out the gas valve until the thermostat is cycled off then on.

It sounds like all your safety features worked properly but that still scares the heck out of you when things go to the limits of safe operation.

I know of no way to protect against this problem. As they say, "do not run out of electrical power". May be a low voltage alarm on the battery system?

Hope this helps,

Jerry

P. S. Attached is some service info on the furnace in case you do not have it.