I have an old Carrier furnace that stopped heating. Thermostat display the time and "AC". 120v and 24v are present on the control board at the furnace. The blower works. I am getting a Service Code 33 on the LED, so I checked the Flame Rollout switch and it seems to be working (ohm meter reads "closed" across the switch). We had a power outage a few nights ago in our area and wondering if this is related. What do I check next? Is there a capacitor for starting the furnace that I should check? Any ideas out there? Thanks.

Word for word, what does the diagnostics chart say for a code 33?

Hi mygirlsdad77,

Here is the error code as listed in the Carrier manual. FYI, we had a large power outage last Wednesday night and I noticed the furnace wasn't working on Thursday morning. I have 120v and 24v being supplied. I also checked the Flame Rollout Switch and that is working as it is supposed to. Thoughts? Thanks for your time on this.

Error Code 33 - LIMIT OR FLAME ROLL-OUT SWITCH IS OPEN - If open longer than three
Minutes, code changes to #13. Flame roll-out switch requires manual reset.
Check for: - Defective blower motor or capacitor.
- Dirty filter or restricted duct system.
- Loose blower wheel.
- Defective switch or connections.
- Inadequate combustion air supply (Flame Roll-out Switch or fuse link open).
- Open Flame Roll-out Switch, or fuse link. Manual reset or replace.

Is this an upflow unit? If so, many time if the furnace is running when the power goes out, the residual heat will trip the auxiliary limit (this limit usually has to be manually reset just like a flame rollout) wich should be located on or near the blower wheel housing. It will be a small switch with two wires going to it and have a small button between the two wire terminals that can be pushed in to reset. Let me know what you find.

Since the code 33 says LIMIT, OR Flame roll-out, and the flame roll-outs check good, Im betting on the limit.