Heater Problem

[fourteener]

I have a factory installed heater in a 2007 2720TM, I believe it is a Suburban Brand, Model NT20SE. We were camping recently and turned our heater on prior to going to bed. Woke up at 2am to the smell of smoke (burning spider webs and dust I presume) shortly followed by the fire alarm and the CO detector. We found out that our battery had ran low (later found out it was low on water), and that the furnace had ignited but the blower didn't have enough power to run.

Two Questions:
1) Has this happened to anyone else?
2) Shouldn't the heater have a safety shutoff that should turn it off prior to getting this hot, as I would have thought it would have simply not started?

Please let me know if you have experienced this and how you fixed, or who fixed.

Oh yeah, everybody is OK, and after charging the battery it seems to work just fine, we simply don't want to chance this occuring again.

[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.

[ShrimpBurrito]

Yikes. So did the flame eventually extinguish on its own, which would indicate the successful operation of the over temperature switch Jerry described, or did you manually turn off the gas?

Dave

[scrubjaysnest]

Originally Posted by ZekenSpider

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.

Our '11 2720SL CO/propane detector also works as a low voltage alarm

[Wavery]

There is one other safety feature. If the battery goes below a certain voltage (I think it's <11.3V) the circuit board should cut off electricity to the gas valve.

The gas valve has an electro-magnetic solenoid that holds the gas valve open during normal operation. Whenever any of these fail safe devices fail, the control board should cut off current to the gas valve. That will disrupt electrical current to the gas valve solenoid and a spring should slam that gas valve shut.

My guess is, your exhaust pipe may be restricted with debris and/or carbon build-up. Carbon can build up in he exhaust chamber if the propane is not burning properly. This can happen due to debris (spider webs, dust etc) in the fresh air intake, on the outside of the camper.

I would suggest taking out the furnace, giving it a close inspection and cleaning of the outside air intake and exhaust and inside air intake and exhaust. You could even have a dead intruder in the exhaust system. Any debris in the exhaust system will burn at a much lower temp than the high-temp cut-out is set at.

If you contact Suburban, they are very good about helping you trouble-shoot your heater over the phone.

If all else fails, the heater is very easy to remove and take to a shop for repair.

Undo the gas line (lower, right front of the heater), undo the electrical connection, remove the 4 mounting screws on the front and pull it straight out. The intake and exhaust pipes will stay in the camper wall as the heater slides out. This will allow for inspection. It may have one screw holding it to the floor but I have removed 4 of these furnaces and never seen that screw used.

This heater is very simple and easy to work on once it is removed. You can test all of the circuits with a multi-meter before removing the heater. Suburban will tell you what the minimum voltage at each connection (or at least they told me).

I've never heard of the fail-safe systems failing to work on these heaters. The back-ups have back-ups. I think that what you may have smelled was debris in the intake/exhaust burning before your battery went low and shut-off the gas solenoid.