again I agree with ennismaple, making syrup in a flue pan alone is flirting with trouble. One thing I do is I use a piece of 3/16 tubing or 5/16 and siphon the nitre out of the bottom of the flues every few boils. My pan does not have a drain for the flues. I am not making syrup in the flue pan, just to be clear. I do this when it's cold before start up. I run it into a 5 gallon bucket with a pre-filter cone and then dump the clean sweet back in. A large basting squeeze bulb will fit on the tubing and be enough to start the siphon.

In cold weather I use a outdoor 100 watt lamp under the flues....good down to 5-10 degrees F.