I ran into this issue mid season last year when i wanted to do a mid season sweep. When i pulled the bottom plate of the cleanout it was full of ice. I had to chip through it in order to sweep. This time, i have been away for two weeks. Last evening i lit the stove and soon after i could see water dripping through the clean out lid. For sure this is rain water. My worry is that if the ice builds up to the thimble water might drip into the stove. Is there any fix to this? Different duravent cap?