I have a Payne 399AV that is about 15yr old. Just started to blow non-stop with no heat. Pressed the reset on the auxiliary limit switch, no change. Looking for flame rollout switch shown in Manual can't find. Had a friend look he couldn't find it either. Am I missing it? Filter hadn't been replaced often enough so it wasn't receiving enough air flow. If there isn't a rollout switch is there something I should look at?

You might look near the top of the furnace.

The main limit switch is likely stuck open. The continuous blower operation is a designed function of an open high-limit. You may be able to get it to reset my tapping on it; normally it resets itself when it cools, but if it has been tortured by repeated and frequent cycling, it may be stuck.

If you will look at the fire wall of the furnace you will see a piece inserted into the furnace, this is the limit switch. One of the wires may have a fuse in it, it will look like a small firecracker, or a diaod. Somehow use a jumper and short around this fuse. If the motor stops running then the fuse is bad and needs replacing.

Here is what I have tried so far. Replaced batteries in thermostat, took the wires off the limit switch attached to the blower and linked them the blower was still going. I'll have to try more tomorrow. Thanks for all of the responses.

The limit switch attached to the blower and the fuse in the wire in the burner don't seem to be the culprit . I would assume then that my main limit switch didn't reset but I didn't have any luck with it. I think I'll call in the pros. Thanks for your help

Cool, but the system may have an overheating condition that caused the switch to keep cycling and eventually stick open. Check your air filter if you haven't already, and keep an eye on the system for the next few days. Replacement of the limit switch would be recommended.