Been using a masterbuilt electric smoker since beginning of the year. The entry level model. Have had good results until........This past weekend, none of the wood chips burned. I noticed very minimal smoke from the vent and found the chips were black but not burned. I always use dry chips. Prior to this, the chips all burned to ash, every time. I have cooked everything on 225 so far and had no issues. Smoker thermostat shows correct and my meat thermometer is correct. Did some troubleshooting and put a regular thermometer inside and that shows good numbers too. Do chips have a shelf life or can they get old and not burn? They were purchased at xmas along with the smoker itself. Chip tray is clean, element is clean, just not burning my chips. Any idea?