I have a Comfortmaker gas furnace from 2001. Model N9MP1050B12A1.
Type FSP. Yesterday morning I noticed the fan didn't stop shortly after the usual heat cycle. I went out to the garage to investigate, & found what I'll call the PVC water outlet line frozen thanks to our new Arctic reality in N.C. Water was spilling out onto the floor from a vertical overflow PVC line up from the point of blockage. Got it unblocked and rerouted away from the low double digit temperatures. No heat since.

Other observations:
A: Gas service to the house is OK. Upstairs gas furnace works fine.
B: Blower fan OK. The only way I can shut it off is at the fuse box.
C: At the Honeywell SV9541M 2094 module: 4 green lights.
Found a Honeywell .pdf online for this explanation:
"Limit string open.Combustion air blower is energized. If control system includes ST9160 Electronic Fan Timer, the heat speed circulating air fan will be energized until the limit string resets."
With advice to Check/Repair:
1. Open manual reset or auto reset burner rollout switch.
2. Open high temperature or auxiliary limit switch.
3. Limit and rollout switch wiring in good condition and securely connected.

I'd like to narrow down the causes & in effect, the solutions based on what I've provided. I suspect the water overflow is at the crux of the problem. As I had no issues prior. I'll need some advice on what the questionable component looks like, as HVAC is not my strong suit.

Comments? Advice? Suspicions?

Thanks for reading.

-John

Kill power.
Recycle power back on. It it works great if not then

Kill power. With a ohm meter or other testing device track down all limits and other control that might have failed then reset if possible and reactivate unit.

Naturally follow the advice give you by the machines blink/flash codes and check them also.

Link to part locations and wiring diagrams.

http://icpindexing.mqgroup.com/documents/086477/44003101003.pdf

One last tip. It is possible that other furnace components froze so Apply some heat (electric box heater etc) to the front of the furnace while the drain line is watched to see if more water flows.

Thanks to your input I have heat! I reset the 3 rollout switches after proving there was no leftover ice in the line. Let me do something nice for you someday. THANK YOU! -John

Glad you got it going.

YOU fixed it. I was just a guy following instructions. Going to go turn it down now. Getting a little warm in here. :-)

Yes but you actually did the fixing. I just hang around here giving pointers in the right direction.