Went and cleaned a PS40 that was shutting down some times a half hour maybe more but seemed to run fine if it made it past an hour or more. Thought to myself a good cleaning, not the POF switch since it did not occur at the initial start up. Cleaned the stove including internal flues and the vent pipe which just empty's into a 8 inch flue (not a fan) but that's the way it was done and in the past the stove has functioned. Test fired the stove no problems, great fire almost white, active. Getting called back because the stove again is shutting down. Question can the POF switch sometimes fail? Can it fail after a normal start up and has been running? I've read you can clean them off with steel wool to remove carbon but I feel in this case since this is my second attempt it should just be replaced.