hello everyone, i have a harmon p61a and its been working great for 3 years but discovered a problem last night.the stove lights fine but if you turn temp down after its been running for hrs. it wont let the fire get low...in other words it stays burning. usually when you turn temp down after 20 min or so the flame is gone and just random red coals left in burn pot... must be a thermostat prob but new to pellet stoves and wondering what or where is the sensor and how to check it or replace.....thx in advance for your help